Mix up the teen fluff of Cruel Intentions with the sexy psychodrama of Fatal Attraction and you've got this summer's last (?) stale thriller. Ben, who's captain of his high-school swim team, belly-flops after cheating on his girlfriend with the new sexy vixen in school, curly-haired Madison Bell (Traffic's pouty-mouthed Erika Christensen). But when he returns to the straight and narrow, Madison loses it and sets her sights on his ruin. Car chases, perverse e-mail stalking, and near-death by drowning ensue. People finally figure out what she did last summer -- just in time to thwart her latest blood binge.

Filmmaker John Polson never asks what mental glitch it is that causes Madison to go psycho when she's dissed by her jockish paramours. We're merely treated to a neat trick -- a screechy sound that says, "Watch out Boyfriend, the Black Widow is about to pounce." The movie would be a mere stinker if not for the creepy performance by the vice-type-cast Christensen, which she clinches with a repertoire of eerily icy stares and relentless resolve. There are no surprises here, but Swimfan is still a diverting dip. (88 minutes) At the Apple Valley, Entertainment, Flagship, Holiday, Narragansett, Providence Place 16, Showcase, and Tri-Boro cinemas.