Big Dam Plot

The Giant Wall of Watery Doom is a pretty scary threat. Consider that a dam needs to contain outright gigantic amount of water, a bit of Monumental Battle, or worse, threat of Monumental Damage can be VERY scary. In the United States, the prototypical dam for this to happen at is Hoover Dam, thanks to The Eiffel Tower Effect and the big potential for Scenery Porn.

That's how you get a Disaster Movie with a Big Dam Plot, where a dam is threatened with destruction or actually destroyed in whole or part. Though a Monumental Damage threat can be very effective indeed, sometimes the attackers do manage to destroy it, or it just happens kind of randomly. In any case, you don't want to stay around.

The outdoor equivalent of the Exploding Fishtanks.

Anime and Manga

 * The whole Yuda arc in Fist of the North Star ends in a dam being destroyed
 * Monster Rancher has The Courageous Seven face this problem in the episode of the same name: Evil Hares see them entering a town and decide to destroy the dam, wiping out the whole place just to take care of them.

Comics

 * In one of the Dark Horse Comics' Shrek issues, Shrek tries to get rid of a dam that has flooded his swamp.

Film - Animation

 * Ice Age: The Meltdown: The melting glacier creates a natural dam as most of the ice melts, leaving a thin wall. The animals try to get to the other end of the valley before it bursts.
 * In Osmosis Jones, the dam is in Frank's nose and it holds not water but mucus. A pollen allergy, compounded by Thrax's sabotage, causes it to break.
 * In Flushed Away, Toad's plan is to open the floodgates protecting the rat's sewer city so that it gets washed away during the World Cup halftime.
 * Team America: World Police uses the Panama Canal to the same effect.
 * In Tiny Toon Adventures How I Spent My Vacation, Buster and Babs' subplot is kicked off when an escalating water fight ends with Babs intentionally opening a dam and flooding Acme Acres.
 * Just right after the Snuggly Duckling scene (and hence the song "I've Got a Dream") from Tangled, Rapunzel and Flynn can actually be seen escaping a collapsing aquaduct when the latter is spotted by the palace guards outside the Snuggly Duckling.

Film - Live-Action

 * The destruction of a Hoover lookalike dam figures prominently in the first Superman movie.
 * The Ents destroy a dam to wash away Isengard in the Lord of the Rings movies.
 * The books have the inverse of this trope: the Ents build a dam to temporarily reroute the river into Isengard.
 * Evan Almighty's climax has a dam breaking to justify the construction of the ark.
 * X 2 X Men United ended up with the destruction of the power station
 * Dante's Peak also has a dam destruction at some point
 * The Dam Busters, as you'd expect. Based on a Real Life example.
 * Force 10 From Navarone: In this Film of the Book (and the original book), a dam is destroyed in order to wash away a bridge and prevent Nazi troops from wiping out a group of Yugoslavian Partisans.
 * In Frankenstein Meets the Wolf Man, one of the villagers blow up a dam to kill the monsters.
 * Our Man Flint. The Galaxy organization uses its Weather Control Machine to destroy a dam.
 * One of the major set pieces in Earthquake is the destruction of a dam.
 * In The Emerald Forest, the natives plan to destroy the dam that's going to flood their forest by singing to the frogs. Kinda makes sense in context... the American hero thinks their beliefs are quaint and plans to use dynamite instead. The dynamite fails, but the dam is brought down in a storm anyway. Did the frogs do it? You decide.
 * The threat of a bursting dam - which will drown the entire town - if one of the elements that adds urgency to the plot of Hard Rain.

Literature

 * In Death Or Glory, Ciaphas Cain finds his ramshackle band of survivors pinned in a canyon between a hydroelectric dam and an Ork army. After discovering a tunnel through a nearby mountain to the other side, he decides to blow the dam to cover his retreat.
 * In Animorphs, the heroes supersize a beaver dam so that they can unleash a Giant Wall of Watery Doom on attacking Yeerks.

Video Games

 * Fallout: New Vegas features the Hoover Dam as a major resource, since it's one of the only sources of power in the Mojave Wasteland. The end of the game involves a huge battle for control of the dam. Your character has to either defend it or take it over depending on which faction they're aligned with, and it's possible to destroy the dam or at least render it unusable.
 * The Grand Theft Auto series seems to love this trope. In both Grand Theft Auto San Andreas and Grand Theft Auto II, there's a mission where you must put bombs into a dam. Besides, the one featured in Grand Theft Auto: San Andreas is an Expy of the Hoover Dam.
 * Speedy Dave's arc in Mega Man Battle Network 2 involves a dam going to be destroyed by explosives.
 * In City of Heroes, the Positron Task Force revolves around the Clockwork, Circle of Thorns, and Vahzilok all hatching plots involving the city dam in Faultline. The finale of the second part – which awards the Dam Hero badge – has all three plans coming together simultaneously.
 * Battlefield: Bad Company 2 includes a multiplayer map involving control of a village beneath a dam. If the Americans win, they blow it up.
 * One of the missions in GoldenEye: Rogue Agent has the protagonist searching and activating a seismic bomb in the Hoover Dam.

Western Animation

 * The Simpsons episode "Brother from Another Series" involves Sideshow Bob's brother trying to frame Bob for destroying a dam he's building.
 * Class of the Titans' second episode ("Chaos 102", part of the three-episode special) has the heroes fighting at the city dam. It's not clear whether the dam is ever actually threatened, though.
 * The Avatar: The Last Airbender episode "Jet" revolves around the titular character trying to destroy a dam.
 * The Smurfs have a dam protecting their village from flooding. Many stories have the dam breaking or threatening to break, like in Smurfette's initial storyline, where she is actually an agent of Gargamel's trying to flood the village.
 * The villain's plot in Scooby Doo Camp Scare involves dynamiting a dam to
 * In the first episode of The Tick, the Idea Men hold the city dam for ransom with explosives.
 * In the Bugs Bunny cartoon "Wet Hare", villain Blaque Jacques Shellaque dams the stream that feeds the waterfall Bugs is using to shower. Bugs keeps destroying the dam and Jacques keeps rebuilding it, until Bugs builds a dam of his own. Jacques blows it up, but Bugs has built a series of dams for him to destroy, leading up to the Grand Cooler Dam. In an inversion of this trope, Jacques' cannon doesn't destroy it; instead, the cannonball bounces back and knocks Jacques into a waiting police wagon.
 * Seen in the "Mega X" episode of the Mega Man cartoon.
 * Tom Goes to the Mayor episode "Bassfest" where the Mayor has the wonderful idea to hold a concert near a dam. A poorly built dam. Tom realizes that the vibrations from the music will cause it to break and tries to warn everyone or at least have the concert moved. But if you're familar with the gist of this show, you know how well that goes.