Gator huntin'.

Alexandre Aja, director of grisly but mediocre fare like “High Tension” and the remake of “The Hills Have Eyes,” has delivered a B-movie worthy of the label (and the grade) in “Crawl,” which combines man’s natural fear of alligators, extreme weather, and Florida.

As a hurricane approaches Gainesville, champion Florida State University swimmer Haley (Kaya Scodelario) is urged by her out-of-state sister (Morfydd Clark) to check on their semi-estranged dad, Dave (Barry Pepper), who lives in the storm’s path and isn’t answering his phone. Maneuvering around police barricades, Haley drives to Dad’s house and finds him unconscious and injured in the crawlspace — where there is also, it turns out, an alligator.

This crawlspace is maybe 4 feet high in some spots. You don’t always have to literally crawl, but you can’t walk (or run) either. There’s a spot behind some pipes too narrow for the gator to squeeze through, where Haley and Dave are safe, but then they’re trapped. Oh, and the crawlspace is rapidly filling with water. Oh, and there is a second alligator.

Written by brothers Michael and Shawn Rasmussen, “Crawl” is serious, not campy, and Aja — true to form — does not skimp on the gore and injuries. (With only two major characters, it is necessary to introduce minor ones to be sacrificed to alligators. ) Aja makes good use of the claustrophobic space, though thankfully we’re not under the house the whole time. If it’s formulaic (Dad used to be Haley’s swim coach; they have some heart-to-hearts; her swimming skills come in handy), it’s also consistently tense and exciting (the hurricane is an excellent secondary villain), and the characters aren’t too stupid. Like an alligator, the movie is efficient, mean, and behaves the way you’d expect. Prepare accordingly.

B (1 hr., 27 min.; R, strong animal violence and gore, some profanity.)