I have this theory that Open Water started as part of the pitch for Fox’s newest reality TV show. Some enterprising sick bastard of a producer figured it would be a hoot to invite independent filmmakers—who, let’s face it, are generally just one bounced financing check from a slot on The Real World: Cincinnati as it is—to make an ultra-low-tech project. But here’s the kicker: The actors would have to be convinced to participate in heart-stopping, potentially life-threatening scenarios for their “art.� It’d be Fear Factor meets The Blair Witch Project; viewers could then vote on which auteur came closest to killing off his cast. Call it That’s Snuff, and you’re knockin’ on the door of a Nielsen ratings blockbuster, baby.

Your leader in the clubhouse for that hypothetical cultural nadir would be Chris Kentis, because—get this—he somehow convinced his two stars to swim with the sharks. Not like as in power-lunching with Harvey Weinstein—as in strapping on a wet suit and volunteering to become human chum. There’d be no mechanical “Bruce,� no Deep Blue Sea post-production CGI killing machines. It would be a chance to see what happens when movie sharks stop getting digital, and start getting real.

That’s the marketing hook for this based-on-a-true-story experiment in digital video suspense, which should lure some curious viewers into 15 minutes of almost unbearable tension surrounded by a lot of tedium. Power couple Susan (Blanchard Ryan) and Daniel (Daniel Travis) have taken a Caribbean vacation. One day involves an apparently harmless scuba diving excursion miles off shore, but—in a display of accounting acumen previously seen only at Enron—the tour guide fails to note that two people haven’t returned before he takes the boat back. Susan and Daniel find themselves stranded without any means of communication, food or fresh water—and did I mention that they have some toothy company?

The earlier Blair Witch reference probably already scared off those who wonder if this latest “scariest movie coming out of Sundance� is a shark bait-and-switch the likes of which pissed off so many Blair haters. In his way, Kentis is playing with the same notions of throwing modern city-dwellers into a setting of pure survival and watching them disintegrate, but he’s far clumsier at making it work. We know Susan’s a workaholic career woman because her various communications gadgets never stop beeping and ringing—and isn’t already time to declare a permanent moratorium on the cell phone as shorthand for the preoccupied urbanite?

The psychological dynamics don’t exactly get more complicated from there. Susan and Daniel—performed at a level of basic indie-film competence by Ryan and Travis—swing back and forth between high-pitched squabbling and all-business attempts at figuring out what to do next. There’s little room for the kind of emotional death spiral that made Blair far more fascinating a piece of character drama than most viewers gave it credit for because they were too busy bemoaning the lack of bejeezus-scaring.

While it takes a hell of a long time, some of that creepiness finally does rise to the surface of Open Water. Much of what makes these scenes work is that Kentis keeps the camera itself above the surface, letting the jittery notion of being brushed by something beneath the waves twist viewers into knots. That makes for a pretty visually unimaginative movie, but it works at building the kind of subliminal dread that will have you swiping at your own ankles as you watch. And by the time Open Water reaches a climactic pitch-black night sequence—with terrified screams punctuated by bursts of lightning illuminating the divers’ plight—your theater armrests may need a good reupholstering.

Yet it’s hard to get past the notion that Open Water is mostly a whole lot of foreplay on the way to the shark fin money shot. It’s not particularly enlightening when it’s being chatty, and seems a bit too smug about its eventual resolution. All that remains, I suppose, is for individual viewers to ask themselves whether it’s worth all the down time to experience those 15 nerve-wracking minutes. The Fox network, for one, is hoping that your answer is yes.