Blake Lively, a swimsuit and a shark — that’s all the titillation and terror most of us will ever want.

“The Shallows” turns out to be just what the summer cinema needed, a little reminder to be afraid to go back in the water.

Horror and action specialist Jaume Collet-Serra (“Orphan,” “Non-Stop”) serves up a harrowing serving of sea food in this simple, somewhat sensible shark-attack thriller.

Clever, funny and gripping, it goes all far-fetched in the third act. But for 75 minutes or so, we’re stuck with a bloodied Blake out on a rock, waiting for high tide to bring a 24 foot shark into her lap to finish his meal.

Lively shows off her between-babies beach bod to good effect as Nancy Adams, a free spirit who bailed out of medical school to find her way to a beach her late mother once frequented.

Anthony Jaswinski’s script establishes her pluck, her back story and her sense of humor as she mangles Spanish communicating with the friendly local (Oscar Jaenada) who drives her to a Mexican cove with distinct off-shore islets guarding its bay.

“Cuidado,” he tells her (“Be careful.”). “Siempre,” she replies. “Always.”

There are a couple of Mexican surfers there. One has a GoPro mini-camera. And we all know what that means.

While they swim for shore at dusk, Nancy goes for the “one last wave.” And we all know what THAT means, too.

Next thing she knows, she’s stumbled into a shark in a very logical place to find one. She’s grievously bitten, loses her board and finds herself on a low-tide islet with only a shark-injured seagull for company.

Corny touches — Nancy talks to the gull, and the shark.

“Where are you TAKING me?”

And she talks herself through the inevitable surgery-on-oneself moment — not for the weak of stomach.

Lively gives Nancy a hint of shock, a touch of panic and a trace of resignation at her situation. She lets us see the wheels turning as the surfer tries to reason her way out of this jam.

Collet-Serra treats us to stunning underwater slo-mo, establishing Nancy’s ease with a board and a wave, and the hint of menace just beneath the surface. The seas are Tanqueray clear, but the bottom is a minefield of jagged rocks, fire corals and the shark we know is on his way.

Things get into the area of “Oh come on” before they’re done. But “The Shallows” never tries to pass itself off as deep. It’s a straight, simple and primal thriller playing with our darkest deep sea fear — getting eaten.

And Lively, with every bruise, cut and abrasion added to her makeup, with every grunt and scream at a fresh injury, puts us on that rock with her, trying to outsmart one pitiless fish between low tide and high.

MPAA Rating: PG – 13 for bloody images, intense sequences of peril, and brief strong language)

Cast: Blake Lively, Óscar Jaenada
Credits: Directed by Jaume Collet-Serra , script by Anthony Jaswinski. A Sony/Columbia release.

Running time: 1:25