"You're gonna need a bigger buoy." No, that's not a line from The Shallows, the pulse-quickening thriller starring Blake Lively as Nancy Adams, a stranded, bleeding surfer who is hunted by a great white shark. But the thought does occur when she scrambles atop a slim buoy, anchored a couple hundred yards offshore, as it's being encircled by her sharp-toothed predator. There's no way that skinny platform can protect her. When the shark begins to hammer the floating life preserver, our worst fears -- and Nancy's -- start to materialize. Nope, it's not gonna be enough -- not nearly enough. So, just how did Nancy get into this predicament? We quickly learn that this blonde, athletic adventurer is a medical-school dropout from Galveston, TX, who is grieving the recent death of her mother. She hitches a ride to a secluded beach in Mexico, where her mom loved to surf, in order to clear her head and figure out her future. Nancy meets a couple of local surfers after being jilted by a hungover friend, but when they leave she decides to catch one last wave by herself. Big mistake: While alone, she's attacked and bitten by a massive shark. With blood flowing from a deep gash in her leg, Nancy manages to swim to a craggy rock, where she uses her medical know-how to stitch up her wound with her crescent-shaped earrings and necklace. She's safe for now, but she's lost a lot of blood and her tiny safe haven will disappear when high tide returns. What to do? The Shallows is Jaws-lite, but that isn't a criticism. While the film doesn't come close to possessing the depth of Steven Spielberg's classic, it does offer plenty of well-earned jolts and scares to satisfy moviegoers looking for escapist summertime fare. Director Jaume Collet-Sera (Orphan, Run All Night) and cinematographer Flavio Martinez LaBiano fill the screen early on with lush images of sand and surf -- and lovely glimpses of Lively's well-toned body -- but when terror strikes and the majestic blue water turns Tarantino red, they heighten the suspense as darkness, literally and figuratively, descends upon our heroine. Nancy is all alone, save for a wounded seagull who provides some deadpan humor and companionship, as the nighttime cold envelopes her. It's a terrifying situation that is made all the more convincing by Lively's perfectly modulated performance. She goes from glamour girl to panic-stricken to fearless over the course of 87 sleek minutes, forcing us see that underneath her smokin'-hot physique is a smart, determined woman who isn't going to allow a bullying shark to turn her into his next snack. The film isn't perfect, however. It's hard to believe that Nancy's friend never comes to look for her, and no shark would act the way the one here does. (Of course, the same is true of the predator in Jaws, which is what produced the drama.) The shark, after having chomped down on three other people and a nearby dying whale (which is what drew it into the shallow waters to begin with), would likely be full and leave poor Nancy alone. But what fun would that be? The Shallows isn't anything more than a high-concept, B-movie diversion, and it doesn't pretend otherwise. You can almost hear the pitch session to the would-be producers: "Blake Lively surfs in a barely there bikini on a secluded, pristine beach in Mexico, where she's forced to battle a nasty great white shark in open water." Who wouldn't write a check for that? Or buy a ticket?