Piranha (1978 film)

Piranha is a 1978 American B movie about a swarm of killer piranhas. It was directed and coedited by Joe Dante and starred Bradford Dillman, Heather Menzies, Kevin McCarthy, Keenan Wynn, Barbara Steele, and Dick Miller. Produced by Roger Corman, Piranha is a parody of the 1975 film Jaws, which had been a major success for distributor Universal Studios and director Steven Spielberg, and inspired a series of similarly themed B movies such as Grizzly, Tintorera, Tentacles, Orca, Monster Shark and Great White.

Two teenagers come upon an apparently abandoned military installation. They take advantage of what appears to be a swimming pool to skinny dip. The teenagers are attacked by an unseen force and disappear under the water. A light activates in the main building and a silhouetted figure investigates the screams, but is too late to help.A determined but somewhat absentminded insurance investigator named Maggie McKeown is dispatched to find the missing teenagers near Lost River Lake. She hires surly backwoods drunkard Paul Grogan to serve as her guide. They come upon the abandoned compound, which functioned as a fish hatchery before being militarized. They discover bizarre specimens in jars and indications of an occupant. Maggie locates the drainage switch for the outside pool and decides to empty it to search the bottom, but the moment she activates it a haggard and frantic man begins to panic and attacks her, attempting to stop the draining until he is subdued by Grogan. The two found a skeleton in the filtration trap of the empty pool, and learn it was filled with salt water. The man awakens and steals their jeep, but crashes it due to his disorientation, and is taken to Grogans home where they spend the night. They take Grogans raft down the river, where the man wakes up and tells them that the pool in the facility was filled with a school of piranhas, and that Maggie released them. They are skeptical until they hear a dog barking and they come across the corpse of Grogans friend Jack, who has bled to death from an attack on a fishing dock. ........

Source: Wikipedia