Garbage. This is one of those SyFy monster movies ala Mega Python vs. Gatoroid but with a much larger budget. It's also a direct Jaws rip-off and steals all of its other scenes from other decent horror films. There is Richard Dreyfuss is a cameo roll singing "Show me the way to go home", the poster has a girl on top of the water with a bunch of piranhas right below her, and there is also the inevitable argument that "we can't close the beach now, this community needs the money!" Remember how Samuel L. Jackson died in Deep Blue Sea? That method has returned.
The lead actor is a newbie with the name Steven R. McQueen, another rip-off. It was good to see Elizabeth Shue, Ving Rhames, and Christopher Lloyd getting work again, but I think there is a reason you don't see Jerry O'Connell very much anymore, he even sucks in this movie. It also has a pair of children who just yell and scream the whole time; that makes for pleasant movie watching.
Kate came home while I was watching this and joined me around the mid-point of it when the fish really get going. She hates horror movies, but I tried to explain this was not a horror movie. This is really making fun of horror movies and trying to use that tactic to make some money for itself. The fish naturally choose spring break to start wreaking havoc and really, there was some sort of morbid satisfaction watching a bunch of frat boys and sororstitutes getting eaten alive by piranhas.
Lessons learned: you can kill a piranha with a shotgun (Ving Rhames), you can tase one to death (Elizabeth Shue), you can transform into a badass hero trying to save lives when you were just a nerdy seismologist diver a minute before (Adam Scott), and your silicone implants float to the surface after piranhas eat your boobs.