Rated R

The best thing that can be said about “Piranha 3D” is that it’s utterly shameless. This is a compliment. Director Alexandre Aja took the worst of all possible scenarios—a remake of a 1970s horror flick (a “Jaws” rip-off directed by Joe Dante) that’s saddled with gimmicky 3D effects—and succeeded thanks to sheer unabashed excess. Like the drunk and disorderly college kids so gleefully eviscerated in “Piranha 3D,” this is a movie that’s ready to party as loudly, graphically and stupidly as it can. It’s big, dumb, tasteless fun of the highest order, the kind of trashy cinematic cheese that barges in to the late-summer movie doldrums, does a keg-stand, pukes on the floor and then passes out in a stupor, but not before making you laugh.

The usual B-movie ingredients are on full display here. The ferocious fish terrorizing everyone onscreen have invaded Lake Victoria, a spring break hot spot that’s placid but for a week of bacchanalian decadence that takes place each year. And so, just as quickly as the spring-breakers guzzle beer and get naked, they’re chewed up by the piranhas in a dazzling array of gruesome fashions. It’s pretty standard stuff, except Aja, who also directed “High Tension” and the 2006 remake of “The Hills Have Eyes,” turns what was supposed to have been a rote exercise into a fever dream of excess. The only way to prepare for “Piranha 3D” is to take some mind-altering drugs and read a stack of “Fangoria” and “Maxim” magazines, and even then, you’ll likely leave the theater asking yourself, “Did I really just see a fish burp up a severed penis in 3D?”

That penis, by the way, belongs to Jerry O’Connell, who stars here as Derrick Jones, a thinly-veiled version of Joe Francis, the sleaze-merchant behind “Girls Gone Wild.” Jones and his crew are in Lake Victoria to capture some spring break action, and they hire Jake Forester (Steven R. McQueen), a local teen, to show them the hot spots. Meanwhile, Jake’s mom Julie (Elizabeth Shue), the town sheriff, is trying to keep the college kids under control and investigate the sudden appearance of deadly fish in the lake.

The story is of secondary concern here, as almost the entire movie is devoted to showing bare breasts (including a very long scene involving nude underwater synchronized swimming) and gaping wounds. Aja saves most of his energy for the elaborately-staged spring break bloodbath that takes up the last 40 minutes. Aja and special effects supervisor Greg Nicotero make the climax as disarmingly gruesome as possible, and the effects are as ludicrous as they are impressive. Limbs fly off and outboard motors wreak terrible havoc on panicking co-eds. “Hostel” director Eli Roth shows up for a brief cameo in which he hosts a wet T-shirt contest and gets his head crushed by a boat. This is only a partial list of the bloody highlights.

The cast is just as gleeful as Aja about their roles in all this monster mayhem. Shue and O’Connell are joined by Ving Rhames, Adam Scott, Christopher Lloyd (as an excitable fish expert) and even Richard Dreyfuss, whose cameo at the beginning of the movie as a doomed fisherman serves as a nice nod to “Jaws.” For a film with such a flimsy script and reliance on bare boobs and gore, the cast has a great comedic dynamic.

As for the 3D, it’s a gimmick that’s run its course, but one that Aja uses to full effect, sending eyeballs, anchors, vomit, breasts and a regurgitated penis hurtling at the viewer. “Piranha” likely would have been just as ridiculously nuts without an additional dimension, but it doesn’t hurt. Like a lot of good B-movies, “Piranha” knows that too much is just the right amount. That kind of excess isn’t everyone’s bag, but for lovers of trashy cinematic cheese, “Piranha” is a hell of a catch.