In Lake Victoria Arizona, a tremor causes the lake's floor to open, setting free scores of prehistoric piranhas. Every year the population of sleepy Lake Victoria explodes from 5,000 to 50,000 for a single, wild weekend - the 4th of July. Lake Victoria sits in the crater formed by a prehistoric volcanic eruption, and when earth tremors tear open a crack in the lake floor, all hell breaks through. Piranhas - a million ravenous, razor-toothed monsters, unchanged since the dawn of time. Unstoppable killing machines acting blindly under one primeval impulse: to hunt down anything that moves and strip it to the raw, bleeding bone.