Sheriff Julie Forester (Elisabeth Shue) and Deputy Fallon (Ving Rhames), investigate an incident involving a missing fisherman, Matt Boyd (Richard Dreyfuss) near a Mesolithic Era Dig near Lake Victoria. After locating his chewed-up body, they send it for an autopsy. While attending to another incident, they capture a live unknown species of fish, which they take for analysis to Goodman (Christopher Lloyd), who informs them that it is a living example of an extinct prehistoric fish known as the Piranha. Fearing an attack on humans during the Spring Break, she attempts to warn everyone to stay away from the waters - albeit in vain - and must use all her resources to combat an all-out attack. While she and her department attempt to deal with this issue, she gets a message that her son, Jake (Steven R. McQueen), (supposed to be baby-sitting his much younger siblings), that he, along with a film cast and crew, as well his girlfriend, Kelly (Jessica Szohr), are stranded abroad a stalled yacht, and may end up being the latest victims to these razor-toothed fish.