[[quoteright:350:[[Art/CartaMarina http://static.tvtropes.org/pmwiki/pub/images/image_064.jpg]]]]
[[caption-width-right:350:[[Film/{{Jaws}} We're gonna need a bigger boat...]]]]

[[HereThereBeDragons Here there be monsters.]]

Since [[OlderThanFeudalism ancient times]], some cultures have had a superstitious fear of the ocean. It was vast and almost completely unknown. It could smash any ship man dared float on it, or sweep it away, never to be heard of again. Oh, and there may have been [[AttackOfThe50FootWhatever gigantic monsters in it]]. Until recent centuries many sea charts were illustrated with mythical and fearsome sea-creatures in unexplored regions, and even today the weirdest creatures on Earth are to be found beneath the waves, and we're still finding more. [[TruthInTelevision Some of them]] ''[[TruthInTelevision are]]'' [[TruthInTelevision pretty enormous, too]] (though they're [[EverythingTryingToKillYou not the most dangerous things down there]]).

There are many flavours of SeaMonster (well, yes, [[IncrediblyLamePun most taste a lot like squid]], unsurprisingly). These subtropes include:
* GiantEnemyCrab \\
[[ExactlyWhatItSaysOnTheTin Really big crabs]]. Well, other crustaceans, too. They all taste a lot like crab, though.
* GiantSquid \\
[[ExactlyWhatItSaysOnTheTin Really big squid]]. OlderThanFeudalism, they have the benefit of actually existing. Makes great calamari.[[note]] Not really. Their flesh contains a lot of ammonia, as they use it for buoyancy.[[/note]]
* KrakenAndLeviathan \\
The epically scaled, humongous world-ending dwellers of the deepest trenches, often with lots of references to [[CosmicHorrorStory Lovecraftian]] or Biblical beasts. Tastes like whale meat.
* {{Megalodon}} \\
This prehistoric beast is great for those who like to buy their Shark Fin soup in economy scale.
* MonstrousSeal \\
When they're not cute, seals tend to be portrayed as heartless killers. They mainly target penguins, but may attack humans as well. Supposed to have very lean meat, with a gamey, iron-y taste almost like organ meat.
* StockNessMonster \\
Those that ape (or more like serpent) the queen of cryptozoology, her royal slitherness the Loch Ness Monster. Said to taste rather exotic, like crocodile meat.
* TurtleIsland \\
Those whose large size combined with a sedentary life in shallower conditions make them liable to be confused for islands. Apparently the taste of giant turtle is meant to be better [[Series/{{QI}} than any chicken, beef, mutton or butter]] and a favourite for long sea voyages.

Please place examples belonging to those subtropes only in the specific page, not here.

See also FishPeople, OurMermaidsAreDifferent, SpaceWhale, GiantFlyer, ThreateningShark, EverythingsSquishierWithCephalopods, {{Kaiju}} and OurCryptidsAreMoreMysterious.



* A series of Jameson Irish whiskey commercials feature John Jameson jumping overboard to retrieve a barrel of booze. A giant octopus is seen reaching towards him underwater in some versions. Viewable [[http://www.youtube.com/watch?v=WOydQFJdx1k here]].

[[folder:Anime & Manga]]
* The Dragonosaurus from a {{Crossover}} movie featuring characters and HumongousMecha from ''Anime/MazingerZ'', ''Anime/GreatMazinger'', ''Anime/UFORoboGrendizer'' and ''Manga/GetterRobo'' was a real ''weird'', gigangic sea monster. Its body was a gelatinous, amorphous blob with a face on it, and several snake-like heads sprouted from it. It was told it was a -formerly believed extinct- Prehistoric monster had mutated cause oil spills polluting the ocean.
* The Three-Tails and Eight-Tails from ''{{Naruto}}'', a giant turtle-crab creature with [[MakingASPlash water-based powers]] and an ox-like kraken monster, respectively.
** There's also a giant squid that was the guardian of an island where Killer B and A trained.
* One of the magical creatures in ''Anime/MagicalGirlLyricalNanohaAs'' from which the [[RidiculouslyHumanRobots Wolkenritter]] took {{Mana}} was a many-eyed giant sea monster that emerged from a whirlpool.
* ''Franchise/OnePiece'', being a pirate-themed adventure, has lots of sea monsters — the Sea Kings being a pretty prevalent example. They, along with a lack of winds, make it nearly impossible to enter the Grand Line from anywhere but the entrance. To put an image in mind, Sea Kings can rival islands in size and usually attack whatever they see.
* ''Franchise/{{Digimon}}'' has an entire group of digimon devoted to this. Of particular note are the Seadramon family, which includes the season one baddie Metal Seadramon, and the enormous Demon Lord, Leviamon.
* In one episode of ''Anime/{{Pokemon}}'', Team Rocket accidentally created a [[{{Kaiju}} giant Tentacruel]], with what they believed was a ''poison''. Misty had to convince it not to destroy a city.
* The monster in {{Creator/Junji Ito}}'s "The Thing that Drifted Ashore" looks like a combination of an eel, a mass of barnacles, and the nightmares of everyone in the world who suffers from thalassophobia. [[spoiler:It's implied to be far from the worst thing out there]].
* ''Manga/FushigiYuugi'' gives us Seiryuu. In his beast form, he is [[OurDragonsAreDifferent a dragon]] with water-based powers.
* ''Manga/SgtFrog'': One episode has several sea creatures crawl out of the ingredients pot and come in contact with [[TransformationTrinket the Flash Spoon]], which turns them into giant sea creatures.
* In ''Manga/MadeInAbyss'', the subterranean Sea of Corpses apparently plays host to a few. Only one is ever seen, an enormous thing that looks like a much larger version of an angler fish. How dangerous it is or how many there are isn't known, since swimming in the sea is usually a one-way trip for different reasons, but it looks more dangerous than anything encountered up to that point.
* [[{{Weredragon}} Elma's]] true form in ''Manga/MissKobayashisDragonMaid'' is a massive one-horned sea serpent with a trident shaped tail.

[[folder: Art]]
* The ''Art/CartaMarina'' of 1539 depicts a sea-serpent, numerous types of gigantic whales, a merman, a marine unicorn, a sea-cow, a kind of giant seahorse, a giant lobster holding a man in his claws, a bizarre "sea-hog", a so-called "sea monk" and various other weird fishes or sea creatures.

[[folder:Comic Books]]
* Giganto/Monstro, the Sub-Mariner's giant whale with arms and legs in ''ComicBook/FantasticFour''.
* A sea serpent appears in ''ComicBook/TheSandman'' story "Hob's Leviathan", part of the "World's End" arc.
* The oceans of Skataris are filled with monsters in ''ComicBook/TheWarlord''.
* So are the oceans and rivers of Elekton in ''ComicBook/TheTriganEmpire''.

[[folder:Fan Works]]
* ''Fanfic/ChildrenOfAnElderGod'': In chapter 4 Asuka fought Amaliel, an aquatic, sea-dwelling monster resembling a viscous blob with tentacles and pincers.
--> ''"...an almost globular torso, with six long sinuous limbs terminating in crab-like claws. From the upper end a subsidiary globe bulged forward bubble-like; its triangle of three staring, fishy eyes, its foot-long and evidently flexible proboscis, and a distended lateral system analogous to gills, suggested that it was a head."''
* ''FanFic/{{Aska}}'' has the [[Myth/NorseMythology Jormungand]] itself.
* ''FanFic/{{Embers}}'': Man-eating Seahorse dragons, leeches that can give hell to the Unagi, and (by chapter 43) something huge that makes Sokka think twice about pentapi. All stem from [[spoiler: the Ocean Spirit's ongoing revenge, and they probably aren't the only things that we'll see.]]
** Add to that list the Isonade, or shark monster, that [[spoiler: Azula faced as she was battling with Makoto.]]
** Walking Whales, a.k.a. the Kadzait. They can grow to huge sizes (the skeleton Zuko encounters is 50 ft. tall), live extremely long lives, and can be good or evil, just like dragons. The Dark ones are known as Sea Serpents.
** In Chapter 78 Zuko defeats a sea serpent banished from his clan for cannibalism of the pods' children.
* ''Fanfic/OneWorld'': Quite a number appear in the story, ranging from the dragon-like Knucker to the mythical Kraken of the north sea.
** GiantSquid: Obviously, there's been one at Hogwarts since the very first book.
** KrakenAndLeviathan: A Kraken attack is blamed for the disappearance and death of Bernard Gibbon and his squib partner. [[spoiler: In reality, they are killed in a firefight with MI-5 Agent Kim Hunter.]]
* Part of the massive danger of the Hungry Sea in ''Fanfic/TheKeysStandAlone: The Soft World'' (as if crazy-making waters and instant thunderstorms weren't enough) is the presence of large and hungry sea monsters.
* ''FanFic/ThePalaververse'': Numerous sea monsters are known to lurk in Theia’s oceans, including carnivorous whale sharks, angel sharks capable of temporary flight, and schools of skeletal bonefish. The deepest, most chaotic abysses beneath the Burning Mountains and the Black Ocean host even stranger things, from colonies of literal spider crabs that spin webs across ocean trenches to Lovecraftian horrors to wild metal-eating Smoozes.

* ''Film/TheBeastFromTwentyThousandFathoms'', a giant dinosaur-like monster that emerged from the sea after thawing out of an iceberg.
* ''Film/{{Jaws}}'' and its host of [[FollowTheLeader imitators]] popularized a combination of this trope and the ThreateningShark in cinema, presenting the largest extant carnivorous shark species, the Great White, as a man-eating monster.
* ''Franchise/{{Godzilla}}'' and related films:
** The bluntly titled ''[[Film/EbirahHorrorOfTheDeep Godzilla Vs. the Sea Monster]]'', where the King of the Monsters faces off against Ebirah, a giant crustacean monster.
** Heck, Godzilla himself certainly applies. In [[Film/{{Gojira}} the first film]], he's even shown sleeping underwater. ''Film/Godzilla2014'' reinforces this aspect of his nature by having the rapid-fire opening credit sequence juxtapose antique artistic depictions of sea monsters in books and maps with {{Retraux}} footage of Godzilla swimming around in TheFifties.
*** Consequently, both ''2014'' and ''Film/ShinGodzilla'' feature visible gills on their respective redesigns for the King of the Monsters.
** Likewise, there's [[Film/{{Atragon}} Manda]], who is a sea-dwelling [[OurDragonsAreDifferent Chinese Dragon-looking guardian of the lost civilization of Mu.]]
** Titanosaurus from ''Film/TerrorOfMechagodzilla'' is another giant aquatic dinosaur. He's generally a NonMaliciousMonster, but an evil scientist mind controls him to help Mechagodzilla defeat the Big G.
** One monstrosity sent to kill the heroes in ''Film/YamatoTakeru'' is the fish-like many-tentacled Kaishin Muba.
* ''Film/ThePhantomMenace'': There's AlwaysABiggerFish on Naboo. First, there's the Opee Sea Killer, a bizarre fish-crab hybrid that catches prey with a long, sticky tongue. Then, there's the larger Colo Claw Fish, a giant sea serpent with clawlike appendages used to capture smaller creatures (including baby Sea Killers, which can however [[HoistByHisOwnPetard chew out of a Claw Fish's stomach to escape]]). And finally, there's the Sando Aqua Monster, resembling a cross between an otter and a newt, but far bigger than the largest whales and the [[{{Kaiju}} biggest predator]] in Naboo, who can and will eat almost anything (including the aforementioned Colo and Opee) that stands in its way.
* The {{Kaiju}} in ''Film/PacificRim'', which emerge from a rift in the middle of the Pacific and swim towards major human cities. The last batch that guard the Rift in particular seem specifically designed for underwater combat.
* ''Film/DeepRising'': Features man-engulfing tentacles that act as though they are independent creatures but are, in fact, attached to one giant mutated cephalopod.
* ''Film/JurassicWorld'': The various prehistoric creatures exhibited in the park include a larger-than-RealLife ''Mosasaurus''.
* ''Film/DeepStarSix'' is primarily about a deep sea construction facility's struggles with an unidentified, armour-plated sea monster, with no perfectly clear analogs to any known sea life.
* ''Sea Monsters: A Prehistoric Adventure'': A 2007 National Geographic movie about the various terrors of the Late Cretaceous seas.

* The Avanc (from the afanc of Welsh mythology) from Creator/ChinaMieville's ''Literature/TheScar'', an absolutely colossal monster hailing from an extradimensional ocean, large enough to pull the floating city of Armada behind it as it swims.
* ''Literature/LordOfTheFlies'' also has the whole "beast from sea" speculation affair.
* The Watcher in the Water from ''Literature/LordOfTheRings'' appears to be something like a giant octopus.
* The sea serpent from ''Literature/TheVoyageOfTheDawnTreader''.
* The creature in Creator/RayBradbury's short story ''The Fog Horn'', which was the inspiration behind ''The Beast From 20,000 Fathoms''.
* In ''Literature/OrlandoFurioso'', two different women, Angelica and Olympia, were offered to placate two different sea monsters -- at least one of which was called an orc. Also, the enchantress Alcina uses a whale as transport.
* ''Literature/{{Discworld}}'': The illustrated novel ''The Last Hero'' features a map of the disk with all sorts of monstrous sea creatures popping up here and there. Then a later illustration shows Mustrum Ridcully fishing... with all those creatures lying in a pile at his feet. Turns out the creatures on the map weren't quite on scale.
* The sentient sea serpents in Creator/RobinHobb's ''Literature/LiveshipTraders'' trilogy.
* In the massive live-action RPG [[ShowWithinAShow tournament]] from ''Literature/TheCaliforniaVoodooGame'', the aliens responsible for all the weird events were stranded on Earth because they'd grown into adulthood since their ship crashed. Their mature forms were those of massive flatfishes more than 50' long, so they could no longer fit into their spaceship. Too bad the players never made it back up to the roof, to sneak a peek at the swimming pool....
* ''Literature/SenseAndSensibilityAndSeaMonsters'', which is essentially ''Literature/SenseAndSensibility'', except everything in the ocean developed a psychotic hatred of mankind.
* Taylor Anderson's ''Literature/{{Destroyermen}}'' takes this trope to an insane level. In this alternate world, the great white shark is a small predator with loch ness style creatures being average size and everything being dwarfed by the monster fish, a sea creature so ridiculously enormous that it could swallow an aircraft carrier in one bite.
* [[Literature/PercyJacksonAndTheOlympians Percy Jackson]] encounters the legendary Charybdis and Scylla in ''The Sea of Monsters'', a random sea serpent in the short story ''Percy Jackson and the Stolen Chariot'' from ''The Demigods Files'', and sees a whole army of them attack Poisden's forces in ''The Last Olympian''.
** [[Literature/TheHeroesOfOlympus The sequel series]], has the main group encounter Ceto, the ''mother'' of all sea monsters (though she certainly doesn't look like one when she shows up), and one of her children, the Skolopendra (which is ''definitely'' a deadly sea monster).
* During ''Literature/GalaxyOfFear'' the heroes visit Hologram Fun World and interact with a simulation of a [[Literature/TheGloveOfDarthVader whaladon]], which is friendly then but [[SwallowedWhole later tries to get them]].
* In Creator/HPLovecraft's short story ''{{Literature/Dagon}}'', the protagonist is traumatized by the sighting of a large, unidentified sea creature. In this case the creature itself never actually ''does'' anything particularly hostile, it's just the complete unfamiliarity with this being that freaks him out. Lovecraft also wrote the better-known [[Literature/CthulhuMythos Cthulhu]], who would also qualify although he isn't necessarily confined to the sea.
* In one of the ''Literature/DoraWilkSeries'' short stories, Eryk is attacked by some sort of sea serpent which crossed over from its plane into our reality. Szelma has to rescue him.
* The Eeeague from ''Literature/TheTraitorSonCycle'' are some sort of tentacled, fairly intelligent creatures that roam the North Cross Ocean. One of them is enough to sink a ship.
* ''Literature/TheWitchlands'' has sea foxes, which are giant, carnivorous sea serpents with heads of foxes. They're attracted to the scent of blood in the water and can crush ships in pursuit of their prey. Most people consider them mythical, but Safi, Iseult and Merik encounter -- and are nearly killed by -- two of them when they're sailing to Lejna.

[[folder: Live Action TV]]
* ''Series/{{Primeval}}'' has featured a few prehistoric sea monsters. Episode 1.3 gave us a Mosasaur, Episode 2.4 gave us a future shark and the Mer, walrus-like sea monsters that appeared to have evolved from primates, and Episode 5.2 gave us a whole pack of Pliosaurs.
* ''Series/MightyMorphinPowerRangers'': The Dragonzord is this in robotic form, rising dramatically from the ocean to wreak destruction upon either the city of Angel Grove, or the forces of evil, depending on who possesses the Dragon Dagger, and whether the rightful owner of the dagger is in control of himself. It is a Godzilla-esque metal beast, and of endurance as yet unmatched.
* The miniseries ''Series/SeaMonsters'' (from the creators of ''Series/WalkingWithDinosaurs'') features some of the nastiest aquatic predators that ever existed in RealLife.
* Since the TropeCodifier of [[Franchise/{{Godzilla}} all Japanese kaiju]] was a SeaMonster, the ''Franchise/UltraSeries'' has lots of marine {{kaiju}}. Examples include:
** Gubira of the original ''Series/{{Ultraman}}'' is a giant narwhal-like beast with [[ThisIsADrill a drill for a horn]] who goes by [[BossSubtitles the subtitle]] "Deep Sea Monster". The giant lizard Gesura, the two-bodied bat-starfish Pestar, and the whale-toad Gamakujira would also count.
** Eleking from ''Series/UltraSeven'' is a PsychoElectricEel kaiju, who, while appearing in a lake in his original series, has appeared in the ocean in other shows. Seven also battled a monster called Guyros, a giant mass of octopus tentacles controlled by the mysterious Nonmalts, while Iron Rocks, a monstrous robot built by aliens from the remains of WW2-era submarines and warships could also be considered one.
** The first episode of ''Series/ReturnOfUltraman'' features a battle between two sea monsters, the sponge-based Takkong and the seaweed-like Zazahn. Later on Ultraman Jack would have to battle several others, including a mated pair of weather-controlling monsters called Seamons and Seagorath, the jellyfish-like Varricane, and the fish-dinosaur mix Muruchi.
** Leilons from ''Series/UltramanTiga'' was a FriendlyPlayfulDolphin turned into a kaiju by nuclear waste leaking into the ocean. Despite now being a giant monster, he still maintains his Friendly Playful personality, even when battling Tiga.
** Series/UltramanDyna battled a sea serpent named Dipras in one episode. Later on, he faced off the aquatic bigger-than-Ultraman alien Spume and its [[GiantEnemyCrab crab-like]] enforcer Reicubas.
** ''Series/UltramanGaia''''s Bokurag was a crab-fish-lizard mix made partially out of water, meaning it was effectively invisible to XIG's monster-detection technology whenever it swam.
** ''Series/UltramanMebius''' Arigera is an eyeless pterodactyl-like kaiju that can glide through seas and skies alike at supersonic speed.
** Maga-Jappa from ''Series/UltramanOrb'' is the [[ElementalEmbodiment King Demon Beast of Water]]. While the characters actually encounter him at a lake, his seahorse-like appearance and ability to render water foul-smelling with his presence suggests he's mainly an ocean monster.

[[folder: Music]]
* A sea monster appears on the cover of Music/{{Asia}}'s 1982 self-titled debut album.
* "The Beast of Pirate's Bay" from the Music/{{Voltaire}} [[https://www.youtube.com/watch?v=wcgvLiNYCcA song of the same name]], which supposedly has a habit of eating careless sailors. [[spoiler:The last verses reveal that it's just a legend that the narrator himself made up, to keep people from disturbing a wounded whale hiding from hunters in Pirate's Bay.]]

[[folder: Myth And Legend]]
* OlderThanFeudalism: Charybdis, from ''The Odyssey'', an unseen monster that swallows and spits out ''the entire ocean'' on a regular basis in the form of a giant whirlpool. Related is Scylla, who lives near the ocean rather than in it and has lots of heads [[note]]Scylla used to be a sea nymph. She was courted by the god Glaucus, but spurned his advances. Glaucus went to the sorceress Circe for a love potion. Circe, falling for Glaucus, turned her "rival" Scylla into a monster in a fit of angry jealousy. Greek Myth: a soap opera, but hardcore.[[/note]]
* Another even older Older Than Dirt example: Tiamat, the primordial sea serpent from the Babylonian creation myth ''Literature/EnumaElish''.
* Many a woman ChainedToARock was to appease a Sea Monster. From Greek legends, Hesione and Andromeda's monsters. Andromeda's was named Cetus, which of course means "whale" now.
** To add insult to Cetus' mortal injury, after Perseus slashed her throat, he delivered the deathblow by showing him the petrifying head of his own sister, Medusa, transforming Cetus into a coral reef.
* The Con Rit, or Tarrasque, a sea serpent claimed to be found in the South China Sea. Some theories say that the possible sea serpent is inspiration to both the Oriental Dragon, and the South African Snake God. [[note]]In French mythology the Tarrasque was originally a tortoise-shelled, eight legged land bound dragon that menaced the French region of Tarrascon (thus the name) until defeated by a female saint. The French drew on this legend for their name for the beast of Halong Bay while Vietnam was still part of French Indochine.[[/note]]
* Literature/TheKalevala has a giant pike and Iku-Turso, a malevolent sea monster.
* Myth/NorseMythology has the Kraken of course. And then there's Jormungandr, the Midgard (World) Serpent, the sea monster to end all sea monsters. An immense sea snake, he wraps all the way around Midgard, holding his tail in his own jaws. He has a major rivalry with Thor, and plays a key role in [[TheEndOfTheWorldAsWeKnowIt Ragnarok]].

[[folder:Other Sites]]
* In ''Wiki/SCPFoundation'', [[http://www.scp-wiki.net/scp-1823 SCP-1823 ("Rock in a Hard Place")]] is a MegaMaelstrom that hunts down ships. There is a large monster with many heads that has attacked the SCP-1823 MegaMaelstrom on at least one occasion. It may be the inspiration for the creature Scylla in Myth/GreekMythology.

* ''Pinball/{{Seawitch}}'' depict two monstrous sea creatures as war mounts — one is a giant fish with fangs and ragged wings, while the other is a barracuda-like serpent.

* Podcast/DiceFunk: One pursues the party throughout Season 2, episode 3. The existence of such creatures is an important plot point.
** It was eventually revealed that there was only one large monster stalking the seas of Lorelei. [[spoiler: It just happened to be a chimera of ''every single sea god in the multiverse''.]]

[[folder:Professional Wrestling]]
* Wrestling/KaijuBigBattel has Unibouzu, a giant urchin and Call-Me-Kevin, an alien who landed in the ocean.[[/folder]]

[[folder: Tabletop Games]]
* ''TabletopGame/MagicTheGathering'' has tons of Sea Monsters. Leviathans, Krakens, Sea Serpents, Giant Enemy Crabs, assorted giant fish and whales... notably enough, they're often both blue and absurdly huge, despite the Blue colour being anything but based on brute force.
* ''TabletopGame/{{Rifts}}'' has boatloads of sea, lake, and even river monsters.
* ''TabletopGame/DungeonsAndDragons''
** Sea Monsters by the truckload: scyllans, krakens, leviathans, ramfish, dragon turtles, sea drakes.
** And then there's Dagon, a lesser-known demon prince who is an eel with the head of a freaky fish, six tentacles ending in clawed hands, and more eyes than I really want to count. Other demon princes are afraid of him.
** The ocean-oriented ''Stormwrack'' book includes many Sea Monsters.
** Older editions had the Behemoth (giant hippo), aquatic "dinosaurs" (Elasmosaurus, Mosasaurus, Nothosaurus, Plesiosaur), dragons (Lung Wang and Yu Lung), Froghemoth, Giant (Crayfish, Crocodile, Eel, Octopus, Sea Snake, Squid, Turtle), giant fish (Afanc, Gar, Pike, Verme), Merrow (aquatic ogre), Mottled Worm (aquatic [[SandWorm Purple Worm]]), Sea Serpent, Seawolf (lycanthrope), and Vodyanoi (aquatic Umber Hulk).
* The ''TabletopGame/{{Warhammer}}'' world has buckets of these, as detailed in the Seas of Blood supplement to the early 90s naval warfare spin-off ''TabletopGame/ManOWar'' and the 2011 Pirate-themed spin-off ''Dreadfleet''. Warhammer's giant sea monsters include the classic giant squid Kraken and the horrific Black Leviathan (a humongous deep-sea angler fish that could swallow small ships whole), as well as the Narwhal-like Behemoth, the giant crab Promethean the Sea Dragon, the giant merman Triton, the Sea Elemental and the giant shark Megalodon. Dreadfleet has its own zombie sea monsters -- the Sea Giant, Bone Hydra and Leechwyrm -- and even a ship made from the rotting undead carcass of an Orb Leviathan (possibly the same species as Man'O'War's Black Leviathan, maybe not). Finally smaller, but still huge, sea monsters are available from Forge World to use in land-based Warhammer armies in the shape of the Merwyrm and its variants, and the Dark Elf army has access to aquatic Hydras, Sea Dragons and the abyssal tentacled fiend Kharybdis.
* ''TabletopGame/{{Warhammer 40000}}'' has a few, though they're rather obscure. The Space Wolf homeworld has a ''massive'' kraken (said to be a [[HordeOfAlienLocusts Tyranid offshoot]]) and sea serpents straight out of Norse myth, appropriate given the Space Wolves' Viking theme, and a sea monster is said to live on the planet Armageddon, where it attacked Ork ships. Given the nature of the setting, it's a safe bet that most world with any oceans have at least one.\\
The "Iron Snakes" chapter has a mostly ocean-bound home world (their fortress-monastery is on one of the moons), and one of the challenges which aspirants wishing to join the chapter have to face is single combat with a sea serpent using only a harpoon and a canoe.
* ''Franchise/YuGiOh'' features many sea monster cards. Most notably are Sea Serpents which are a whole monster type, and many Water monsters can count.
* ''TabletopGame/{{Monsterpocalypse}}'' has the Tritons, whose main monsters are kaiju-sized sea creatures.
* ''TabletopGame/{{Exalted}}'':
** The armored terror (that's the actual in-universe name) is a thirty-foot-long carnivorous fish covered in armor-like scales and provided with a beaklike pair of fangs easily capable of severing limbs. It normally hunts fish in shallow water, but it's perfectly happy to go after boats and people. Physically, it sounds a lot like an oversized ''Dunkleosteus'' (
** Benthic knifeooths are serpentine sharks up to twenty feet long. They are aggressive predators and will attack almost any prey they come across, and the mere sight of one swimming near the surface is enough to drive sailors into a terrified panic.

* Several in ''Toys/{{Bionicle}}'', particularly the Mahri Nui arc, including [[InherentlyFunnyWords Gadunka]]( basically a [[MoreTeethThanTheOsmondFamily giant, toothy mouth]] with small limbs attached), a 300-foot long eel-thing, and [[NinjaPirateZombieRobot cyborg sharks]].

[[folder: Video Games]]
* The Water Dragon from ''VideoGame/{{Okami}}'', [[spoiler: which turns out to be the king of the Dragonians]].
* The Sapphire Drake BonusBoss of ''VideoGame/{{Wild ARMs 4}}'', which the player first sees preying on ''another'' sea monster.
* ''Franchise/{{Pokemon}}'': A fairly common archetype for [[MakingASplash Water-types]].
** Kyogre, the creator and master of the seas, fills the "[[KrakenAndLeviathan colossal primal sea monster]]" niche.
** Gyarados is a ferocious, destructive sea serpent that can level cities, and evolves from the somewhat pathetic [[MagikarpPower Magikarp]]. Milotic is considered its benevolent counterpart of sorts, due to the fact that it's also a serpent, it has a much calmer temperament and it evolves from an equally weak Pokemon as Gyarados, though it is much rarer.
*** Gold/Silver/Crystal features a Red Gyarados (most are blue) rampaging in the aptly-named Lake of Rage. In the game a red Gyarardos evolves from a golden Magikarp.
** While not itself a Water-type, Lugia, known as the Diving Pokemon, resides deep within the seas of the Whirl Islands and is said to be the "guardian of the seas." It has the ability to control the weather, most notably it can calm and give rise to storms.
** ''[[VideoGame/PokemonSunAndMoon Sun and Moon]]'''s Wishiwashi are, individually, very small and weak fish. However, they have the ability to school together in sync to form a giant, powerful fish-like monster [[TheWormThatWalks still visibly composed of individual fish]]. School Form Wishiwashi are very powerful, enough so to be known as the Demon of the Sea by local Alolans. Even Gyarados flee from these things!
** Other examples includes various {{Giant Enemy Crab}}s (Kingler, Crawdaunt, Clawitzer), giant ghost jellyfish that attack ships that pass through their territory (Jellicent), a mini Loch-Ness monster thing (Lapras), a large sea-horse [[AllThereInTheManual that whips up whirlpools by yawning]] (Kingdra), a vicious torpedo shark that can tear open supertankers (Sharpedo. [[ExactlyWhatItSaysOnTheTin Yeah]].), numerous prehistoric sea monsters (Lileep, Anorith, Kabutops), killer crocodilians (Feraligatr) and artillery-wielding cephalopods (Octillery).
* {{VideoGame/Earthbound}} gives us the Kraken, a fire-breathing sea serpent. It's considered TheDreaded of [[PortTown Summers]], and [[ThatOneBoss for good reason]].
* The Sega arcade shooter ''VideoGame/TheOceanHunter'' has its share of giant sea creatures, the biggest of which serve as boss and mini-boss fights.
* ''VideoGame/LaMulana'' is maybe the only video game to use the Babylonian interpretation of Tiamat (fierce ocean goddess) rather than the TabletopGame/DungeonsAndDragons interpretation (five-headed dragon queen).
* ''VideoGame/TeamFortress2'': The Demoman considers the Loch Ness Monster to be his mortal enemy, and he accidentally [[SelfMadeOrphan killed his adoptive parents]] in an attempt to [[MadBomber blow it up]].
* Del Lago from ''VideoGame/ResidentEvil4'' resembles some kinda giant newt.
* ''[[VideoGame/BanjoKazooie Banjo-Tooie]]'': The boss of the [[UnderTheSea obligatory underwater level]] is Lord Woo Fak Fak, a gigantic lanternfish who literally lives in Davey Jones' Locker. He can [[ThatOneBoss be a bit tricky]], but is much easier to fight if you use the Submarine transformation.
** Also in Jolly Roger's Lagoon is a giant fish that swallowed Merry Maggie the barmaid. Strangely, it doesn't try to attack you, even when you knock all the teeth out of its mouth in order to rescue her.
* There are some large aquatic creatures in ''VideoGame/WorldOfWarcraft''. Notable examples include Ghaz'rankha, a giant hydra that's a boss in Zul'gurub raid instance (gaint hydras also appear as bosses in Zul'zarrak and the Underbog), and The Lurker Below, a boss in Serpentshrine Cavern raid whose ingame model is actually called "kraken". Some of the larger naga may count for this trope too, their queen Azhara most certainly does.
** Hydra in ''World of Warcraft'' are lizards with three heads. They have two legs and a heavy tail, so they basically move on a tripod as well. Normal ones are about the size of a wooly mammoth or so, but bosses are a little bigger. The Lurker Below is big enough to be a genuine kraken, and three other things in the game share its same ingame model: two similar wild animals related to specific quests and a sea goddess.
* Every creature in ''Videogame/TheAquaticAdventureOfTheLastHuman'' is this.
* Kraken herself shows up as a boss in a few ''Franchise/FinalFantasy'' games. ''VideoGame/FinalFantasyX'' also features a few since your characters are now able to fight underwater. Geosgaeno who is one of the first fiends you fight definitely qualifies -- he's a BonusBoss later in the game. The GiantFlyer Evrae turns into this the second time you fight him, though he's also a zombie. There's also a couple of Sinspawn fiends that you have to fight underwater.
* ''Franchise/SuperMarioBros''
** ''VideoGame/SuperMario64'' introduced Unagi the giant eel [[note]]who has since made appearances in ''VideoGame/NewSuperMarioBros'' and ''VideoGame/MarioKartWii.''[[/note]] and the Sea Dragon -- who actually lived in an underground lake. The Sea Monster's name is "Dorrie", although in Japanese it's name is "Doshi", which is a parody of the Loch Ness Monster and Yoshi since the nickname "Nessie" in Japanese is "Neshi".
** ''VideoGame/SuperMarioSunshine'' had a boss named Eely-Mouth, who was more goofy-looking.
* Niptra of ''VideoGame/ArcanaHeart'', an ancient fish that became the largest and wisest fish in the seas through cycles of {{reincarnation}} before [[AscendToAHigherPlaneOfExistence finally becoming the]] [[MakingASplash Arcana of Water]].
* The Shiguras from ''VideoGame/DarkCloud2'', extremely reminiscent of Franchise/{{Pokemon}}'s Lapras. [[MadScientist Dr. Jaming]] intends to use them as tools for his own nefarious purposes, and goes as far as to enslave one of them, Pau's friend, Shingala.
* ''Aquanaut's Holiday'' has several whales swimming in its oceans, but there's also an enormous prehistoric fish floating in the southwest corner of the map.
* ''VideoGame/MonsterRancher'' had the Zilla, a freaky whale/gorilla hybrid.
** And Lesione, which is a [[RidiculouslyCuteCritter much cutesier]] Plesiosaur-like creature with elements of trained marine mammals.
* Morpheel in ''VideoGame/TheLegendOfZeldaTwilightPrincess''
* One of the later puzzles in ''VideoGame/{{Azada}}: Ancient Magic'' requires you to free the Baron (Munchausen) from a giant sea monster's mouth.
* ''VideoGame/MonsterHunter'': ''Monster Hunter Tri'' introduced mechanics allowing your character to swim and fight underwater. Obviously this introduced a whole slew of new aquatic monsters, including a lightning-spewing serpent/crocodile mix and a large, grotesque Angler Fish capable of perfect camoflage, blinding flashes of light and inflating into a spined ball. There is also a marine Elder Dragon that is a football field long, and causes earthquakes with its horns.
* A boss in ''VideoGame/MetroidFusion'' is Serris, a sea serpent capable of SuperSpeed.
* ''VideoGame/ShadowOfTheColossus'' features two: the electric eel colossus that is [[PrimalFear frankly terrifying]], and the wading lake monster, which is terrifying AND [[AIRoulette frustrating]].
* ''VideoGame/EndlessOcean: Blue World'' features several prehistoric creatures to be encountered, one of whom even tries to attack you. There's also lots of benign marine life which have monster-esque names, such as a large giant squid named "Kraken Jr." and an albino sperm whale named "Leviathan". Sadly, all of the prehistoric creatures are relegated to cutscenes only and cannot be swam with.
** Actually, Kraken Jr. is the giant squid's child -- he's actually quite small, but he may still count since he'll eventually ''grow'' into a giant.
* Expansion packs for the original ''VideoGame/ZooTycoon'' allow you to raise and exhibit plesiosaurs and Loch Ness Monsters. Not together, though: they eat each other's eggs!
* ''VideoGame/{{Tradewinds}}: Legends'' and ''Odyssey'' have several sea-monster battles, both bosses and random encounters.
** Also, in the ''Legends'' CaptainsLog: "Fought kraken. Looking for good calamari recipe."
* ''VideoGame/CobraTriangle'' featured several different sea monsters to include a GiantEnemyCrab, a GiantSquid, sea serpents and [[ThreateningShark giant shark]] [[spoiler: as the final boss]].
* In the third chapter of ''VideoGame/GrimFandango'', Manny ends up on the bottom of the ocean, which is pitch black except for a single light source. Upon finding another traveler, trying to walk to the other side of the ocean(and failing at it by walking in circles for years), Manny gives him a warning.
-->Manny: Watch out for sea monsters.
-->Chepito: Oh, these guys?
-->Chepito shines his lamp at the ocean, revealing wall-to-wall, creepy-looking sea monsters just behind the darkness. The darkness you are walking through. Try not to think about that during your remaining time under the ocean.
* This is the entire point of the [[ExactlyWhatItSaysOnTheTin World Monster Fishing]] mode of [[http://www.facepunch.com/threads/1093537-PS1-Big-Ol-Bass-2-(AKA-EXTREME-FISHING-THE-GAME) Big Ol' Bass 2]], an obscure but awesome fishing game. You can catch everything from [[EagleLand bass with the American flag colors]] to [[MonaLisaSmile a trout with the Mona Lisa on it]], from [[ThreateningShark a shark]] [[PantheraAwesome with a leopard design]] to [[spoiler:[[UpToEleven Dinosaurs]]]].
* VideoGame/TheElderScrollsIVOblivion has the [[ExactlyWhatItSaysOnTheTin Giant Slaughterfish]].
* In ''VideoGame/TheSims2'', in Neighborhood View, a sea serpent would sometimes be seen randomly at the end of the river (near Gunther Goth Highway) and disappear into the bay.
* ''VideoGame/SunlessSea'' has a lot of these living in the dark waters of the neath. Most of them are bigger than your ship. And then there's the Eye, which either belongs to an enormous one of these or something far, far worse.
* ''VideoGame/GodOfWar'' series loves this trope. But again, the games are based on Myth/ClassicalMythology:
** The Hydra from the very first game and the very first boss. It is a serpent with lots of heads just like in Classical Mythology, the games are based on.
** The Kraken in the second game. He looks similar to how he looked like in the ''Film/{{Clash of the Titans|1981}}'' but with classical elements thrown into the mix as well.
** Hippocampi, the water creatures of Poseidon, in ''God of War III''.
** Scylla in ''Ghost of Sparta'' looks like a hybrid of different sea creatures, including a shark, a squid, a crab and a narwhal.
* ''VideoGame/DwarfFortress'':
** Sea monsters are a kind of creature that spawn in evil oceans (any biome can be good, neutral or evil in-game). As the game is text-based they don't have a visible appearance, but the game describes them as having multiple eyes and arms, as well as two pincers. They're fearsome enough in the sea, but cannot move if stranded on land. When dwarves like them, they do so for "their horrifying freakish appearance".
** There are also sea serpents, which resemble limbless dragons and can spawn in any ocean.
* ''{{VideoGame/Subnautica}},'' naturally. As of now, there are four "leviathan-class" creatures which are utterly enormous, and three of them are extremely hostile. There's also the reefbacks, which are so big that [[MeaningfulName small ecosystems]] [[ExactlyWhatItSaysOnTheTin grow on their backs]]. There are also plenty of smaller (but still large) creatures that evoke the image of a sea monster, many of which are also happy to hunt you down if they get wind of you.

* ''Webcomic/{{Juathuur}}'' has the Vriths, ugly, bizarre creatures.
* The White Steel Eels and Flying Wales from ''Webcomic/TowerOfGod'' are obviously sea monsters [[FlyingSeafoodSpecial flying through the air]].
* ''Webcomic/{{Homestuck}}'': A couple of [[RaisedByWolves lusii]] fit the bill.
** Gl'bgolyb, a [[EldritchAbomination titanic, tentacled horror]] that dwells deep beneath the Alternian seas, and whose scream [[BrownNote would kill every troll alive in the galaxy]]. She was also the one responsible for raising the [[FantasticCasteSystem magenta-blooded troll empresses]].
** The sea goats, a.k.a. [[FanNickname goatdads]], giant, amphibious half-goat half-fish creatures that can move on land like seals. One was Gamzee's [[ParentalNeglect always absent]] parent, spending all its time journeying at sea. Jake English later met another, which proved to be extremely vicious and aggressive.
* ''Webcomic/ChampionsOfFaraus'' has sea serpents, and one named Serpentus antagonizes the main characters when they need to investigate why he's expanding his territory.

[[folder: Western Animation]]
* ''WesternAnimation/AvatarTheLastAirbender''
** There is a reason that the Serpent's Pass was called such, which the characters find out first hand when the giant sea serpent came out when they tried to cross.
** The giant lion-turtle with an island on its back.
** And the Unagi that lives near Kyoshi Island.
*** Which feeds on [[CallASmeerpARabbit elephant]] [[ExactlyWhatItSaysOnTheTin koi.]]
** During the Season 1 finale, the ocean spirit [[OneWingedAngel assumes the form of a]] huge, humanoid, Franchise/{{Godzilla}}-esque monstrosity.
* Cecil the Sea-Sick Sea Serpent from ''WesternAnimation/BeanyAndCecil''
** Bad guy Dishonest John had an undersea craft disguised as a giant cephalopod, known and feared far and wide as Billy the Squid.
* ''Franchise/CareBears'' had a sea serpent named "Shaky" who needed work on his confidence.
* ''WesternAnimation/{{Catscratch}}'' features a Kraken, which Gordon must fight in order to wish for a longer tail.
* The giant Nautilus of ''WesternAnimation/{{Cybersix}}''. She beats it by dropping a bridge on it, literally.
* The pilot of ''WesternAnimation/TheDrinkyCrowShow'' involves whales, which is appropriate because it's set on a whaling ship. The whales are drawn in the style of those really old maps with "Here be dragons" written in the corners.
* ''WesternAnimation/DuckTales1987'': The sea monster that ate Scrooge [=McDuck's=] ice cream is actually a submarine colored to resemble an orca.
* ''WesternAnimation/DuckTales2017'':
** In the pilot episode, the cast encounter a few of them on their way to Atlantis, including a GiantSquid, a bunch of [[OurMermaidsAreDifferent scary-looking merducks]], and what appears to be a storm elemental.
** In "The Spear of Selene!", a tentacled monster named Charybdis is guarding the temple of Ithaquack. [[spoiler: It's a PunchClockVillain that protects the Spear of Poseidon and is very polite with those seeking a different artifact.]]
* ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' features Steven Magnet, an AmbiguouslyGay river serpent whose hysterics over having his "look" ruined by the lost of half his mustache cause our heroes a problem in the [[Recap/MyLittlePonyFriendshipIsMagicS1E2ElementsOfHarmony second episode]]. In "[[Recap/MyLittlePonyFriendshipIsMagicS5E9SliceOfLife Slice of Life]]", he even refers to himself as a "sea monster" — despite having only been seen in a river.
* ''WesternAnimation/SpongebobSquarepants'': When Spongebob yells that there are sea monsters on the beach to keep people out of the water, an erudite serpent reminds him that "we sea monsters have made great strides in the fields of science and literature."
* In ''WesternAnimation/StarWarsCloneWars'' the Mon Calamari fought the separatist forces with knights riding on giant eels.
* ''WesternAnimation/StarWarsTheCloneWars'': In the episode ''Bombad Jedi'', [[TheScrappy Jar-Jar]] [[TheBeastmaster made friends]] with a Kwazel Maw, a giant, aquatic centipede-like beast native to Rodia. Technically a Swamp Monster, but Rodia's swamps are so wide and deep they're effectively a freshwater ocean.
* ''WesternAnimation/YellowSubmarine'' had a Sea of Monsters.
* Unsurprisingly, the world of Mer featured in ''WesternAnimation/ThePiratesOfDarkwater'' is full of Sea Monsters, including Darkwater itself, and the huge, serpentine Leviathans.
* ''WesternAnimation/PopeyeAndSon'' episode "The Sea Monster" is about ExactlyWhatItSaysOnTheTin. The monster is friendly and befriends Junior.
* Episode "The Unsalted Sea Serpent" of ''WesternAnimation/{{Babar}}'' has a big menacing sea serpent and its baby offspring living in the local lake.
* ''WesternAnimation/{{Kaeloo}}'': In Episode 78, the gang, who are pirates in this episode, come across a giant sea monster which has several tentacles. [[MakesJustAsMuchSenseInContext For some reason]], its face looks exactly like Mr. Cat's.

[[folder: Real Life]]
* If one takes the vast scope of the Earth's history, many of the well-known mythological or legendary "sea monsters" [[TruthInTelevision do have basis in reality]]. Some huge water dwellers which resemble sea monsters are listed below:
** GiantEnemyCrab - The Japanese spider crab of course, whose legspan may grow between 12 and 18 feet in total length. The creature itself weighs over 40 lbs. However, the prehistoric ''Jaekelopterus'' was far more massive, attaining lengths of up to 8 feet with and weighed possibly close to 400 lbs, though it is more lobster than crab.
** GiantSquid/[[KrakenAndLeviathan Kraken]] - ExactlyWhatItSaysOnTheTin - of course, the present-day {{GiantSquid}}, which can grow over 40 feet in length, as well as its larger cousin the [[UpToEleven Colossal Squid]]. The Giant Pacific Octopus should qualify as well, since large specimens may reach an impressive 20 feet across. Some ancient mega-cephalophods include Tusoteuthis, a 30-foot ancestor of the present-day vampire squid, and the "Giant Orthocone" ''Cameroceras'', a cuttlefish-looking creature which resembles a cross between a squid and a snail.
** [[KrakenAndLeviathan Leviathan]] - Most whales largely resemble the whale-like depictions of the biblical Leviathan, though the ancient species ''Livyatan melvillei'', named after the famous {{Creator/Herman Melville}} of {{Literature/MobyDick}}, deserves special mention, as it is much like the modern Sperm Whale, but with far larger 14-inch teeth. It would have been the [[BehemothBattle chief (and probably the only) rival]] of the equally-sized giant [[ThreateningShark shark]], {{Megalodon}}, as both lived around the same time and the same place.
*** For depictions of the Leviathan as a great fish, we have:
*** The Whale Shark, of course, which grows from 30 to 40 feet in length with a weight of over 20 tons - almost the length of a school bus, and twice the mass.
*** The Oarfish - an enormous eel-like creature which can reach lengths of 30 feet - is considerably eerier in appearance, and looks like the more sea serpent-themed depictions of the Leviathan.
*** The ancient ''Leedsichthys'' was perhaps the largest fish of all time (challenged only by {{Megalodon}}) and most updated estimates put it somewhere between 50 or 60 feet long. It looks amusingly like a supersized version of a common ray-finned fish.
*** ''Dunkleosteus terrelli'' is an extinct creature that is probably the best example (aside from sharks) which is a fish, incredibly large, and monstrous (so much so that it is hypothesized to be a cannibal to its own species). It is believed to have the strongest bite force of any vertebrate alive or extinct. It could grow up to 30 feet long.
** {{Megalodon}} - Like the Giant Squid, this is a straight-up real creature, albeit no longer existing ([[OurCryptidsAreMoreMysterious supposedly]]). It is hypothesized to have looked liked a Great White Shark - but around three times longer - and its famous jaw reconstructions could easily fit several people inside (not surprising for an animal whose bite could have crushed a small car). It was 50-60 feet long and weighed around 50 tons.
** {{Monstrous Seal}} - Yet another straight-up real animal. The Elephant Seal in particular is the biggest of the lot, growing 16-20 feet long and weighing 3-4,000 kilograms (that's right - [[CaptainObvious an Elephant Seal may grow to the]] [[ExactlyWhatItSaysOnTheTin size of an elephant!]]).
** {{Stock Ness Monster}} - The extinct Plesiosaurs, more-or-less. Additionally, they are mainly saltwater dwellers, adding to their "sea monster" image. The largest species, ''Elasmosaurus'', could reach 46 feet in length.
*** Other huge marine reptiles include the 69-foot ''Shastasaurus'', the largest of the ichthyosaurs ("fish lizards"); ''Mosasaurus hoffmani'' - a terrifiying apex predator which could grow 56 feet long (the largest known lizard species of all time); and the 49-foot ''Pliosaurus funkei'' ([[NamesToRunAwayFromReallyFast Predator X]]), also a superpredator.
** {{Turtle Island}} - Though it doesn't exactly resemble an island, the 12 foot ''Archelon'' is a candidate for the largest turtle species of all time, as well as ''Stupendemys'', which was slightly shorter but possibly heavier.
* And including extinct animals, we have [[UsefulNotes/StockDinosaursNonDinosaurs plesiosaurs and similar creatures]] like the ichthyosaur and mosasaur, and {{Megalodon}}, a prehistoric shark the size of a whale. Its modern counterpart may be the Whale Shark, which is thankfully nonaggressive and feeds on plankton. Indeed, so many different creatures like this existed in the past that one can argue that plesiosaurs can't have survived to the present, because ''the mosasaurs would've eaten them'', long before the K-T extinction took down subsequent forms of reptilian SeaMonster. The modern equivalent of ''Carcharocles megalodon'' might be the Whale Shark from a size perspective, but in every other respect it's basically a Great White that is... bigger.
* [[http://en.wikipedia.org/wiki/Pliosaurus Pliosaurus]]. Its teeth are each a foot long.
* The Oarfish: an eel-like fish that can exceed fifty feet long. Harmless, but quite impressive.
* The African country of Burundi is home to Gustave, a well-known man eating crocodile. Gustave weighs in at approximately one ton, is approximately twenty feet in length, and has been known to eat adult hippopotami. Given the number and variety of bullet-shaped scars which cover his body, it's quite possible that he's ImmuneToBullets.
* Saltwater crocodiles can be even larger than Gustave. Large adult male saltwater crocodiles can be more than six meters long and weigh more than 2,600 lbs.
* Prehistoric crocodiles were [[AlwaysABiggerFish even larger]] than saltwater crocodiles. ''Sarcosuchus imperator'', ''Deinosuchus riograndensis'' and ''Purussaurus braziliensis'' were around ''forty'' feet long or longer, and all of them weighing around 7-8 tons.
** Many of them were also fully marine. ''Plesiosuchus'' was basically an orca sized marine crocodile that looked like a shark.
* [[http://en.wikipedia.org/wiki/Bloop The Bloop]], or rather, whatever made the Bloop, an ultra-low frequency underwater sound that matched the profile of a living creature, but not any specific living creature we know. If it did come from a living creature, scientists agree that it would have to be several times larger than the Blue Whale, the largest known animal on earth. Interestingly enough, the signal originated from a point in the South Pacific roughly 950 nautical miles from [[Franchise/CthulhuMythos the sunken home of another large monster.]]
** [[DoingInTheWizard Sadly]], the Bloop is [[http://www.pmel.noaa.gov/vents/acoustics/sounds/bloop.html now thought]] to be the sound of an iceberg breaking up, rather than a living thing.
* ''Tullimonstrum'' (informally called the Tully Monster), [[http://news.yale.edu/2016/03/16/solving-mystery-tully-monster a bizarre fossil lamprey]] from the Carboniferous Period, bears a striking external resemblence to the Loch Ness Monster, except it's barely a foot long and found in North America.
* The Coelacanth is a person-sized carnivorous fish that has been swimming around virtually unchanged for millions and millions of years. It was thought to have been extinct until live specimens were caught in the 20th century.
* The whole point of fishing shows like ''Series/RiverMonsters'', ''Hooked'', and ''Monster Fish''. Their catches range from the modest (Taimen), to the bizzare (catfishes of the Amazon), to the truly gargantuan in scale (marlins, giant catfishes, and the Mekong Giant Stingray).
* The basking shark, second-largest living fish, can grow up to thirty-plus feet. They also look rather monstrous, cruising through the water with their three-foot mouths. Fortunately for all mankind, [[GentleGiant they and whale sharks eat only plankton]]. They are also the source of a few sea monster myths, where the decomposing bodies of these sharks after having beached or caught as by-catch have been mistaken for plesiosaurs.
* Sperm whales and giant squids are among the most famous modern day examples. They even engage in {{Behemoth Battle}}s!
* Several deep-sea species of shark are also quite large. The megamouth shark grows to eighteen feet in length, and the Pacific sleeper shark can grow to fourteen, though ichthyologists theorize they may grow as long as twenty-three feet. Related to the Pacific sleeper is the Greenland shark. It lives [[CaptainObvious in Greenland]] and closer to the surface, routinely grows to seventeen feet in length and has been found with ''parts of polar bears in their stomachs.''
* Lion's mane and Nomura's jellyfish can grow to gigantic sizes. The lion's mane can grow nearly forty feet long and the Nomura can weigh over four hundred pounds. Nomura's jellyfish have also marked off an important check on the "to-do list" of most sea monsters; sinking ships, albeit in a passive manner. "Blooms" of these jellyfish have numbered in the thousands and at least one fishing vessel has been capsized after trying to haul up a net full of these jellyfish.
** The largest lion's mane to wash up had tentacles in excess of 120 feet. That's longer than a blue whale, usually considered the largest organism. Now imagine encountering that while deep-sea diving... [[ParanoiaFuel knowing its transparent, poisonous tentacles are all over the goddamn place in a huge radius...]]
* ''Syringammina fragilissima.'' It's a deep-water denizen eight inches across. It's not very impressive-sounding, but suddenly becomes more so when you find out it's a ''single-celled organism''.
* ''Livyatan melvillei'' is a prehistoric sperm whale named after both the leviathan and Moby Dick via Melville. It earns the name by having the largest teeth of any known organism. It ate other whales and probably competed with Megalodons. Yikes.
* Several species of pliosaur, including the so-called Predator X, were roughly whale-sized, but with jaws more resembling those of an alligator.
* Several deep sea fish are very bizarre and monstrous in appearance, with huge jaws filled with hundreds of needle-like teeth. Fortunately they tend to be very small compared to humans.
* The very first one in history was the 600-million-year-old ''Anomalocaris'', frequently dubbed the world's first apex predator. It was only about a meter long, but in comparison to the other creatures of the period, that's {{Kaiju}}-sized. Some of its relatives were pretty big too, like the filter-feeding ''Aegirocassis'', which was 2 meters long.
* Research done in 2014 revealed that {{Stock Dinosaur|s}} ''Spinosaurus'' was likely a freshwater variant on this trope, using short, ducklike hind limbs to paddle its way through rivers and eating large fish out of the water with its long crocodile-like jaws. For reference, ''Spinosaurus'' itself was ''sixty feet long'', and its prey would have included fish as big as or bigger than grown humans.