A young surfer named Nancy (Blake Lively) is stranded 200 yards from shore at a secluded beach after being attacked by a great white shark. As the shark circles her rock, she must figure out how to get to safety. (  / Sony Pictures)

It’s helpful to think of “The Shallows” — the spare yet serviceable new shark-themed thriller starring Blake Lively — as less of a 21st-century “Jaws” than a distaff version of “127 Hours.” Like that 2010 drama, which notched James Franco an Oscar nomination for his portrayal of an increasingly desperate hiker whose arm has become wedged between a boulder and a canyon wall, “The Shallows” is essentially a one-person show, in very close quarters. For most of the movie, Lively’s character is stranded on a rock 200 yards off of a remote Mexican beach after being bitten by a great white shark while surfing. That beast, rendered in convincing CGI, continues to circle her menacingly, as well as somewhat inexplicably, considering (a) she has no meat on her bones; (b) it has just eaten three other people; and (c) there’s a buffet of rotting whale carcass a short swim away.

As packaged by writer Anthony Jaswinski and director Jaume Collet-Serra — best known for the Liam Neeson thrillers “Unknown,” “Non-Stop,” “Run All Night” and the forthcoming “The Commuter” — this fish tale gives off something of a Moby-Dick stink, due to the giant hook that appears to have become lodged in the critter’s lip. This makes for an angry — and scary — monster, and the film establishes a nice drumbeat of mounting tension and dread.

Nancy (Blake Lively) travels to a remote beach where she finds herself faced with a great white shark in “The Shallows.” (Courtesy of Columbia Pictures)

Lively, however, is probably not going to win any awards for her performance, which mostly consists of screaming in agony as her character, a med school dropout named Nancy, performs emergency surgery (using a couple of pieces of jewelry) on the nasty flap of thigh meat that has been all but torn away. There is almost no dialogue, other than Nancy talking to herself or to the injured sea gull — a fellow shark victim — with whom she shares her precarious ocean perch. “Are you still out there?” Nancy mutters to her marine tormentor, at just about the movie’s halfway point.

Like “Jaws,” there’s a lot of waiting around for the inevitable water-churning climax.

All that said, it’s still nice — really nice — to see a film about a woman in jeopardy who turns out to be resourceful and brave. The camera may linger at times a bit too long on Nancy’s bikini bottom or on the décolletage of her neoprene wet suit jacket, but she’s no helpless damsel in distress. That’s as refreshing as a dip in the ocean. Collet-Serra has a good eye for scenery, too. Although the surfing sequences are merely adequate, the beach setting is beautifully shot, even in the scariest scenes.

Is “The Shallows” a thriller for the ages? No, but it’s decent popcorn fare. It’s about as deep as the titular lagoon on which it’s set, but the breakers promise a short and heart-pounding ride, with no wipeout.

The Shallows (85 minutes, at area theaters) is rated PG-13 for graphic, bloody images, including do-it-yourself surgery, intense sequences of peril and brief crude language.