It's spring break time on Lake Victoria and the town has been taken over by a bunch of college students who apparently have watched too much MTV and have been born without the gene that keeps you from acting like a naked, boozy asshole in public.
The sheriff (Elisabeth Shue looking very healthy indeed) slowly begins to realize somethings off when she finds the body of Richard Dreyfuss dead and rather chewed up due to his opening scene encounter with the vicious prehistoric piranha. These tireless fish have escaped an underground lake cracked open via seismic activity and have set up shop in the more quiet Lake Victoria above. Meanwhile her son (from The Vampire Diaries Steven R. McQueen - seriously, that's his name?, I mean really...) leaves his younger siblings behind to take take a day job with a sleazy Girls Gone Wild like producer. Meaning of course that eventually every single character we've been introduced to will have a run in with the people eating fish for a big cute children in peril finale.
The movie delivers the half naked people, the fully naked people, the blood, the gore, and all the sorts of debauchery it promises. I'm not a big fan of gore, and I flinched a bit at times - but the overall effect is so relentlessly entertaining I just had to enjoy myself. It's far from classic cinema, but it's a well made B-movie and doesn't really try to be anything more. The 3D was fun enough - not sure you completely need it - but it certainly didn't take me out of the experience - and probably added somewhat to the sleazy feel of the film in a good way. Just don't expect the genre defying nature of Tucker & Dale vs. Evil or the perverse hilarity of Splice and you'll likely have a good time if the trailer appeals to you.
Oh, and Christopher Lloyd is in it too for some key exposition about the beasties. 'nuff said. Only thing left to mention is my personal tip that if a swarm of man eating sea life is bearing down on you, probably not the best idea to "encourage" the female acquaintance who's trying to pull you by repeatedly calling her a f'ing bitch. Didn't seem to help in the film - seemed unlikely to help in real life.