I think by now we've all figured out that there's not much chances of watching a better 'shark' film than Jaws. That's a 37 year old film by the way. But in the last decade there's been a few good tries, most notably, Chris Kentis' nerve-wrecking Open Water and The Reef.
Dark Tide suffers from a lengthier running time than actually necessary, a sleep-walking appearance by Martinez and a low-budget (the latter is kind if debatable as it adds to a surprising sense of realism). It has its merits. The underwater shots are brilliant and look and feel real. The characters are decent enough with veteran Ralph Brown being the best of the bunch as the super annoying millionaire Brady and the climax is agreeably tensed. The critics hated it but personally i have watched much much worse.