Piranha (1978)

Heather Menzies (Maggie McKeown) is a private investigator hired by the parents of Barbara Randolph (Janie Squire) to investigate her disappearance. With the help of Paul Grogan (Bradford Dillman), they discover a military installation with a salty water pool. Whilst investigating the pool, they empty it to discover human remains at the bottom. However, unknown to them, they have released genetically engineered piranhas that have been made to like in the waters of this climate. Their only hope is to stop them at the dam down the river. Chasing the piranhas down the river, they encounter death and carnage as the piranhas eat everything in their way, humans, animals, and even boats. But can they get to the dam in time and stop them, before they reach a summer camp where children, including Paul’s daughter, are engaging in water activities?