The film starts out with two idiot hikers breaking into a posted "No Trespassing" government facility, they see a huge tank of liquid and just jump in. It could have been a pool full of giraffe urine, but these fuckers don't care. Ends up instead of giraffe urine it was actually full of salt water and mutated piranhas.
A investigator is sent to find the two idiots so now she breaks into the facility and without consulting anybody drains the pool into a river. In my opinions that makes her responsible for the death and injury of every person who ends up getting attacked by the piranhas. Anyway now the fish are loose and they just eat the fuck out of everybody. They even somehow kill a dude who was sitting on a dock with his feet in the water. Hint: pull your goddamn feet out of the water!
It goes on like that until the end. Blood, zero CGI special effects, brief nipples, funky 70's bodies, humorous attack scenes, funny pronunciation of the word "piranha". Worth a watch, but just don't expect too much. My biggest complaint is there were no hot chicks. P.J. Soles was at her hottest in 1978 (one year before ROCK N ROLL HIGH SCHOOL) and she would have added some much needed excitement that this film lacks.
It will take that asshole all day to inflate that lounge.