One of the quickest, easiest ways to establish an alien world as being very unlike Earth is to make its "water" some wacky colour, or give it some other unusual features or appearance. It's not always explained exactly what kind of chemicals or minerals are causing it to look this way, but regardless, it's still perfectly able to support the native flora and fauna (though that doesn't mean it is safe for Earthlings). See also Alien Sky, which serves the same purpose and may accompany it — the Earth's oceans are the same colour as the sky due to similar refraction, so if the sky and sea don't match you must be someplace exceptionally alien. Alien Landmass is another sister trope, often used for the same reasons. Compare Waterfall into the Abyss. Contrast All Planets Are Earth-Like.
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Anime and Manga
- The oceans of Namek in Dragon Ball Z are green (and the vegetation is blue).
- Used in the Neon Genesis Evangelion movies:
- By the ending of The End of Evangelion, the sea has turned into red-orange LCL, liquified human rests resulting from the Assimilation Plot, containing their merged souls.
- In the Rebuild of Evangelion movies to highlight the ecological damage to Earth post-Second Impact: the sea has literally turned red with blood.
- In The Space Trilogy, the waters of Malacandra have the peculiar quality of very pointy standing waves and are literally blue (not just reflective of the sky); the seas of Perelandra, on the other hand, are orange, and have floating mats of seaweed on which 'land-dwelling' life grows instead of islands.
- The Amoebic Sea, of Wayne Barlowe's Speculative Documentary Expedition (and its adaptation Alien Planet) is actually a living gelatinous colloid of microorganisms. The edge of the sea towers over the surrounding beach.
- Solaris depicts a strange planet completely covered by a multicolored sea, which is actually one living, sentient organism. There were two film versions of the book which also contained this sea.
- The Dragaera series reveals in passing that the ocean is orange, although it's unclear if this applies to the whole thing or just the portion that's blanketed by the Overcast.
- The Monster Blood Tattoo series, set in a bio-alchemical-punk fantasy world, has strongly acidic, multicolored oceans that are the result of exotic salts from the sea floor dissolving into the water. Swimming in it is unhealthy: in half an hour you will have a really bad rash, and over an hour and a half will kill you. Not to mention that there are colossal monsters and kraulschwimmen that stalk the sea lanes and prey on ships and sailors.
- In Animorphs, the Yeerk homeworld is covered with huge lakes of what look like melted lead, where the Yeerks live in their unhosted state. Leera, meanwhile, is mentioned having oceans so clear that you can see for miles.
- In Sergey Lukyanenko's third novel of A Lord from Planet Earth trilogy, aptly named Sea of Glass, all bodies of water on a remote uninhabited planet appear to be made of dust or sand. In fact, the water is perfectly consumable and hydrating, but it only turns to liquid when ingested by someone, although it does feel a bit like eating sand at first. It's a strange curiosity that no one has bothered to study since humanity is too busy fighting a war with a Blue and Orange Morality enemy. The final Combat by Champion takes place on this planet on the shore of a "sand" sea. The protagonist manages to deliver the killing blow, and then both his and the enemy's blood mixes and contacts the "water", which starts a chain reaction that turns the entire sea into regular liquid water.
- In the Skylark Series, the planet Osnome has literally blue oceans. This is because they are an ammoniacal copper sulphate solution - copper being exactly what the protagonists are in search of.
- In the Humanx Commonwealth Verse, the planet Quofum is best known for two things: being prone to disappearing and having oceans that are 9% alcohol.
Live Action TV
- In a scene in Star Trek: Deep Space Nine various characters compare the tint of the oceans on their homeworlds. Earth's are blue. Bajor's are green. Trill's are purple.
- The Great Link resembles a reddish ocean, but it's actually billions of Changelings in liquid form, intermingling with each other.
- The Doctor Who story "Mindwarp" opens with the TARDIS landing on the beach on a planet where the ocean is bright pink.
- "The Keys of Marinus" attempted it first: Marinus had sands of glass and seas of sulfuric acid.
- Call of Cthulhu
- Campaign The Fungi from Yuggoth, adventure "Halls of Celaeno". The fourth planet of the star Celaeno (in the Pleaides) has a grey ocean.
- Fragments of Fear (second Cthulhu Companion), adventure "Valley of the Four Shrines". The PCs can use a Crystal Ball-like device to view the gray Lake of Hali where Hastur the Unspeakable lives (a planet circling the star Aldebaran).
- Dungeons & Dragons
- Adventure Q1 Queen of the Demonweb Pits. One of the alternate worlds the PCs can visit from Lolth's Web is a planet with a pink ocean.
- Rocket Age's Mars has silt seas, where the old seas of water slowly dried up and filled in as the planet's ecology collapsed.
- In Werewolf: The Apocalypse, Lady Yul's Malfean abode is a multicolored sea of toxins
- In Exalted, the sea of the demon realm of Malfeas is an intelligent, acidic, and very, very bitter Yozi named Kimbery, the Sea that Marched Against the Flame.
- In Blades in the Dark, the sea is ink-dark with occasional hints of star patterns.
- Kerbal Space Program has Eve, with its purple oceans (which may be partially made of rocket fuel.) Averted with Laythe, which from some angles looks as if you might still be on Kerbin.
- While never explicitly stated, the oceans of Age 233 from Riven are known to be highly acidic. For one thing, Gehn collects his water from a giant bowl on the roof. For another... well, try and guess the range of the tidal zone◊.
- From the same series (and game), Riven has water that is more of a gelatinous colloid suspended in a mesh of microorganisms that are noticeably afraid of heat.
- Multiple Ages - Spire, Relto, and Kadish Tolesa among them - have a 'sea' consisting of a thick layer of fog.
- The enormous lake surrounding Ae'gura in Uru was filled with algae that caused it to glow in the dark 3/5 of the time, producing a day/night cycle. Until the algae were wiped out, of course.
- The 37th Age has a sea filled with 'dark currents'; when the seawater mixes with the freshwater that flows from the rivers of the one charted island, it releases a thick mist which the inhabitants worship as The Whiteness.
- Torus' twin "seas" are connected through the hole in the centre of the ring; driven by a force of unknown origin, the water on one side drains through an enormous whirlpool and into an enormous fountain on the other, where it gushes into the upper atmosphere, evaporates, breezes to the 'edge' of the ring, and condenses and falls as rain.
- In Populous, four of the terrains have differently-colored substances that function the same as water in the others: Rock & Lava has red lava, Bit Plaius has floating letters spelling BULLFROG, Cake Land has caramel, and Silly Land has a checkerboard pattern.
- Natural seas in Spore can be blue, green, or red.
- The Special Stages in Sonic CD are set on islands on other planets, each with a different color ocean.
- The Jade Sea of Guild Wars is literally made of Jade due to Shiro transforming a normal sea with the Jade Wind. The waves are now frozen in place in the form of pure Jade as is the maelstrom known as Unawakening Waters.
- Bizzarely fish such as kraken, carp, rays, jellyfish and crustacians still live on the Jade Sea's surface though have(with the obvious exception of crustacians who already have legs) sprouted legs(carp and rays) or have taken to floating(kraken and jellyfish).
- Evolva: The sea that appears during levels 9 and 10 is mentioned in the manual as being made of acid, and it proves it by being instantly lethal, should you dive into it.
- The various Lands in Homestuck feature rivers and seas made of things like magma, oil, blood, paint, and tea.
- In Phaeton Carbonia has seas of amniotic fluid like material, which makes it oceans breathable to humans, interestingly enough the air is toxic to humans as well.
- SCP Foundation, SCP-2264 ("In the Court of Alagadda"). The city inside SCP-2264 is surrounded by a black ocean. The nature of the liquid is unknown but it appears to be more viscous than water.
- The Pirates of Dark Water had the beautiful, bizarre, and geologically unstable alien water-world of Mer.
- Saturn's moon Titan has black seas composed of a mix of ethane and liquid methane rather than water, and reflect the orange-brown sky. Needless to say, it is not an environment that would be well suited for human life.
- Jupiter's moon Europa and Saturn's moon Enceladus are both suspected of having massive oceans hidden under miles of surface ice.
- Earth can give the impression of not being itself in places, too:
- Lake Tahoe is noted for its unusual color. The water appears to change from gold to green to blue to purple depending on the depth.
- Similarly, Emerald Bay.
- The Laguna Colorada in Bolivia is a red lake. No, really.
- Ho'okena Beach on Hawaii's Big Island is one of the few gray sand beaches in the world.
- Morning Glory Pool in the Yellowstone National Park used to be an example. It had originally been rainbow-colored◊ because of special bacteria that lived in the hot spring water, but because visitors threw trash into it which clogged the natural hot water entries, its color is slowly fading◊, with estimations that it will soon be just another common hot spring.
- Elsewhere in Yellowstone, the Grand Prismatic Spring is also rainbow-colored and the largest hot spring in the United States.
- There is also the Lake Retba or Lac Rose in Senegal and this lake is pink. The color is caused by strange bacteria and, oddly, salt content.
- The mountain Kelimutu as three lakes on it's top, each with a different color◊: one is black, one is turquis and one can range from red to blue depending on the minerals in it.
- The Blood Falls of Antarctica, which is a crack in a glacier out of which a large sea of dark red water is flowing, making the glacier look like it's bleeding. The coloration is due to the micro-organisms which live in the water, which have been frozen for millions of years inside the glacier.
- Fairly recently, in 1980-90s palaeontologists asked themselves: what were the ancient seashores like? Real ancient, pre-Cambrian and early Palaeozoic. Current consensus is that without higher plants wind and water erosion went really fast, and land was very flat low plains with occasional vertical rocks. There was no such thing as riverbeds, water flowed into seas as an even layer all over the shoreline. Sediments were carried far into the sea, resulting in far stretches of shallow waters. There was no distinct border between sea and dry land, no shoreline, just kilometres of shallow pools and mud, that got slightly wetter at high tide. Creatures like modern mudskippers would thrive in such environment. Even in the deeper areas, a great deal of iron was suspended in the water, turning the water a sickly green color. It wasn't until certain unicellular organisms began producing oxygen as a waste product that the iron content of the oceans dropped considerably (due to the oxygen rusting out the iron), turning them to their current blue hue.
- As explained on the Alien Sky page, the color of the daylight skies of other planets vary depending of the type of star they're orbiting. As oceans reflect the color of the sky, this mean a habitable zone-planet orbiting a star hotter than the Sun would have even bluer oceans than ours and conversely if said star was cooler its oceans would look from a washed-out blue to white and even orange.
- The oceans of lava theorized to exist in planets that orbit very close to their stars such as CoRoT 7-B or Kepler-78b.
- Venus can be said to be covered in a sea of supercritical carbon dioxide thanks to its large atmospheric pressure and hot temperature.
- Last, but not least, for something really alien the global oceans of metallic hydrogen that form the bulk of Jupiter-like planets, or especially the oceans of liquid diamond with bergs of diamond too, that likely exist in the depths of Uranus, Neptune, and similar planets.