The Threatening Shark doesn't need to show itself in full; the shark's dorsal fin sticking above the water is an iconic image in itself.
This can be subverted when a character falls in the water, sees a fin (or many fins) sticking out of the water and promptly imagines, "Oh, Crap!, a shark! Gotta beat it!" However, most of the time it's just someone pulling a prank by swimming under the water with a fake shark fin strapped to their head or back. Or it may be a Friendly, Playful Dolphin. This, in turn, may end up a Double Subversion when the characters don't fall for it, but then it turns out to be a REAL shark. Or, more comedically, a Devious Dolphin.
- Effectively subverted in this ad called "Rethink the Shark", from a campaign aimed to put deadly shark attacks into perspective.
- Played with in Mahou Sensei Negima! when the class takes a trip to an island. Negi is put 'in danger' so Asuna will make up with him after a falling out. The 'sharks' turn out to be Ku Fei and Natsumi in diguise.
- Arlong from One Piece, who is a shark fishman, does this during his battle with Luffy.
- Later in the series, Hody Jones weaponizes his dorsal fin by putting a blade over it to slice through things as he swims.
- JoJo's Bizarre Adventure Vento Aureo has the Stand named Clash, which takes the form of a metallic shark. It can teleport between and dive into any open liquids, no matter how small or shallow, and in certain scenes where it appears its dorsal fin is the only thing visible, poking out of things like a soup bowl, puddles of water, and even the tears rolling down someone's cheek.
- Literal inversion in The Good Dinosaur. When the pterosaurs make their second appearance, their mouths are seen first, sticking out of the clouds, evoking this trope turned upside-down.
- While the armed men are patrolling the beach watching for the shark, a fin appears in the water, and people panic and flee the water. When the men in the boats approach the fin, it turns out to be kids with a fake fin pretending to be a shark.
- At other times in the movie, the real shark's presence is revealed by its fin appearing, such as when it attacks the boats in the estuary/pond and while Brody, Hooper and Quint are out on the ocean hunting it.
- Airplane! in a Stock Parody of Jaws had the tailfin of the airliner slicing through the clouds.
- Subverted in Percy Jackson and the Sea of Monsters, when Percy, Annabeth and Tyson are stuck in a small lifeboat, and start seeing what appears to be shark fins, circling around. They soon find out they AREN'T shark fins at all: They're teeth.
- In Open Water, the first signs that things are going to get really bad for the couple that's been left behind by their diving boat is the brief shot of a shark fin.
- Deep Blue Sea: The sharks' dorsal fins breaking the water surface is sporadically used to betray their presence. However, this is played with in one scene. Susan is wading through a partially submerged corridor to retrieve the MacGuffin from her laboratory when a shark seems to approach her from behind, but it turns out to just be a harmless shark model. Then seconds later, she sees a second fin, which turns out to be the real deal.
- The Meg:
- As usual for shark movies. Megalodon's especially large fin provides the main characters an easy way to track the gigantic shark from the surface, as well as a Mass "Oh, Crap!" moment when it goes below the water...
- More humorously, when Meiying is playing by herself, she walks past a roomba floor cleaner that someone on the research station seems to have provided with a mini shark fin as a joke.
- In a Nancy Drew Files book, as Nancy escapes from the boat where she and her friends are being held captive, intending to swim to shore for help, the first sign of serious trouble is a shark fin gliding through the water. She forces herself to get over her fear and swim to shore as fast as she can.
- The Doctor Who Christmas Episode "A Christmas Carol" has one scene where a flying shark maneuvers through fog, and its fin is the only visible part of it.
- One of the stories on the I Survived episode that focused on Hurricane Sandy was of a man swept out to sea from his home. He realized how dire his situation was upon seeing a fin pass by him.
"I didn't know if it was a shark or a dolphin and I wasn't going to wait to find out.'
- MAD Magazine had a feature that played with this. Among other things, it showed a shark with a sinister look on his face approaching a beach while "hiding" his fin under an old box, a shark near a large city beach with graffiti on the fin, and another with a brave guy diving off a boat to hunt the shark with the tiny fin. Once he's underwater, he's greeted by a HUGE shark who, apparently purposely kept only the very tip of his fin above the surface.
- In Sherman's Lagoon, Sherman, an actual shark, does this occasionally. His crab friend does it for kicks to scare the hairless beach apes.
- One of Calvin's hilariously morbid snow sculptures in Calvin and Hobbes involved a snowman being chased by a pack of sharks portrayed as fins protruding up from the snow.
Hobbes: Snow sharks?
Calvin: That guy's a goner.
- Secret Agent: Some water pools have sharks in them, shown as a shark fin. However, since the protagonist has Super Drowning Skills anyway, the sharks are just for show.
- Mega Man Battle Network 6: In DiveMan.EXE's scenario, in the aquarium's computer, there are security systems in form of shark fins that will wander around, either trying to get you or just patrolling certain areas.
- In Animal Crossing, sharks can be distinguished from other fish by their fins above the water, but sunfish do it as well.
- Mario & Luigi: Superstar Saga: The beach has a pair of enemies that play with this. One is a skeleton land shark. The other is just a cheep-cheep wearing a large fin. Together they attempt a Shell Game to mess with the player.
- Gyorgs in The Legend of Zelda: The Wind Waker first appear this way, before they try to ram your ship.
- These are a standard enemy in ToeJam & Earl. Opening the Earthling present while surrounded by water will always result in one, sine they're the only enemy to appear in water. Frustratingly, there's a Game Genie code that grants immunity to most damage note , but if you're hit in or near water while using said cheat, the game crashes, making sharks very dangerous indeed.
- The Simpsons:
- Done in "Itchy And Scratchy Land" by Homer when the family is at the beach. Homer wears a fin attached to his back, causing the beachgoers to run away. Then when Bart swims up right next to him doing the exact same thing, Homer screams, "AHHHH! Sharkboy!" and runs away.
- Played With in another Simpsons episode, a Treehouse of Horror story titled "Night of the Dolphin" about killer dolphins. Lenny is out for a night swim and gets surrounded by fins. He's scared that they're sharks, "the assassins of the sea", but they're just friendly dolphins, "the clowns of the sea" — who proceed to kill him.
- Rocket Power: Done by the main characters because of the overcrowding at the beach. However, this backfires when they are not permitted at the beach. They end the ruse by attaching the shark fin on a plank of wood at sea, which is discovered by officials.
- In the classic Disney short "No Sail", Donald Duck and Goofy are stranded on a boat and shark fins start circling them. Goofy lifts one fin and finds nothing underneath. Donald tries the same, but comes face to face with a real shark.
- Looney Tunes:
- In an early short, Porky Pig and his cat are out fishing when a flying fish decides to have some fun and sticks its side fin out to look like a shark's fin. The cat catches on and grabs the fin, but that time the shark was real.
- In the Bugs Bunny cartoon "Wet Hare", villain Black Jacques Shellaque sees a fin on a stream and figures it's one of Bugs' tricks. He dives in to get Bugs, but finds an actual shark instead.
- Another Looney Tunes short, Porky's Naughty Nephew, has Porky's nephew Pinky using a toy sailboat to simulate a shark fin during a swimming race, which scares Porky into swimming fast and winning the race. When Pinky tells Porky that the fin was fake, Pinky lifts it up to reveal a real shark, sending both fleeing.
- In one Humphrey The Bear cartoon, Humphrey takes the keel from a toy sailboat and wears it on his head as a fin to scare away fishermen and keep the fish for himself.
- Subverted twice in an episode of Arthur that takes place at the beach. Sue Ellen spots what she thinks is a shark, but it turns out to just be Mr. Ratburn doing the backstroke. She sees another fin and panics, thinking it's a real shark this time. It's a dolphin.
- My Little Pony: Friendship Is Magic: An intentional subversion in the Cold Open of "Leap Of Faith": it's actually Big Mac, of all ponies, giving Apple Bloom a scare right after she's asked if she'll ever be scared of the water in response to Granny Smith telling how she engaged in dangerous High-Dive Hijinks in her youth.
- In the Roger Rabbit short Trail Mix-Up, Roger ends up in a lake and is scared away upon seeing a shark fin. It's then revealed to be Droopy, who quips "Gets him every time."
- Despite its prevalence, this trope rarely appears in real life. Most sharks ambush their prey by coming from beneath them, even in shallow water. So whilst a fin may tip you off that a shark is around, it's probably just the shark inspecting you. It's when you can't see it any more that you need to start worrying...
- This photo went around the world like mad a while back. It's really a surfer and a dolphin, but that's not why it was popular.
- In the Tommy Bartlett Water Show at Wisconsin Dells, they have (or at least used to have years ago) a scene where a "shark" approaches the performers, represented by a shark fin floating on a piece of wood which is towed by fishing line towards the performers.
- Any aspiring Troll can find these in strap-on form in your local superstore for all your pranking needs.