Though it was once a wholesome, family-oriented attraction, a water park owned by Chet (David Koechner) now features a nudist pool and aquatic strippers. Chet's daughter, a marine biologist named Maddy (Danielle Panabaker), is unhappy about the changes but is powerless to stop the grand reopening. However, when a school of ravenous, prehistoric piranha migrate over from nearby Lake Victoria, Maddy must somehow prevent the park's patrons from becoming fish food.