A shark. A bikini. A Blake Lively. Sign me up. The Shallows is the ingeniously simple thriller that puts Lively on a beach and in the water, squaring off against a ruthless shark that keeps her from making it to shore. Entertaining until it becomes increasingly ridiculous, The Shallows is worth a dip.

Lively is no Tom Hanks—her near-solo performance isn’t going to be raved about for years to come—but she’s a good fit for the role, a beautiful actress who has the presence and determination to overcome a rather vanilla script and make the movie her own. While The Shallows doesn’t shy away from one of its greatest marketing asset—Blake Lively in a bikini—the movie is much more than, well, Blake Lively in a bikini.

Director Jaume Collet-Serra (Unknown, Non-Stop and Orphan) does a fine job bringing Anthony Jaswinski’s story to life by patiently developing Lively’s character Nancy before kicking things up a few notches. The photography is gorgeous—The Shallows is full of beautiful scenery—and at an efficient 86 minutes, the movie doesn’t outstay its welcome. Operating on a relatively conservative budget, Collet-Serra wisely goes the Jaws route and keeps the shark off screen for much of the film’s runtime.

The Shallows, of course, isn’t Jaws, and where the film falters is its inability to maintain a high degree of tension. The film holds your attention throughout, but you never really feel that Lively’s life is in danger—after all, as the sole protagonist, you know nothing can happen to her until, possibly, the final minute.

The ending is marginally exciting, but the film’s left-turn into absurdity saps some of its potential. Lively’s escape through a sea of stinging jellyfish is questionable at best, and I literally laughed out loud at the finale.

The Shallows is a decent thriller that makes good use of its star, but its ludicrous third act holds it back from being anything more substantial.

Review by Erik Samdahl unless otherwise indicated.