Thinking about doing a little scuba diving this summer? This movie might suck the air right out of those plans. It's not just that ''Open Water'' tells the story of a vacationing couple who are eerily stranded in the middle of the ocean while diving. It's also based on a true story. And there are real sharks. Lots of them. (You won't find a single CG effect here -- so there, ''Spider-Man 2''!) ''My wife [the film's producer, Laura Lau] and I heard about an incident that happened off [Australia's] Great Barrier Reef in the '90s, and it sent a chill down my spine that something like that could happen,'' recalls Chris Kentis, who shot the film primarily off the coast of the Bahamas for less than half a million dollars on digital video. ''It's interesting, this arrogance that we'll always be okay [on vacation], just because there's a Club Med or whatever. And everyone has issues about being abandoned and helpless.''
Apparently: When ''Water'' screened at Sundance in January, audiences devoured it, with some dubbing it ''Jaws''-meets-''Blair Witch.'' (Lions Gate then snapped it up for over $2 million.) But Kentis promises his flick is not some low-budget ''Jaws'' rip-off. ''It's not a shark-attack film,'' he says. ''Certainly we have a lot of sharks, but they're just another part of the ecosystem.'' Star Blanchard Ryan agrees. She even brazenly shed her anti-shark chain mail during filming when it proved too uncomfortable. ''Our sharks are incidental,'' she notes. ''If anything, this movie proves that it's not like you jump in the water and sharks come up and kill you.'' We'll take her word for it.