Okay, here goes.
Red Ocean
It is, of course, Die Hard ... under water!
A boat manned by marine biologists - out on a diving expedition to find the mythical Gorilla Shark Squid - is hi-jacked by terrorists who force the divers to search for a gold-laden ship wreck. One of the divers is the ex-wife of former Cop 'Hook' MacLine. MacLine, of course, happens to be on holidays and, in a misguided attempt to win back his ex-wife by "accidentally" bumping into her under water, literally drops in to free the hostages by taking on the terrorists from below. Will he manage to free everybody and kill all the bad guys before he runs out of air? A thrilling adventure packed with slowed-down action and almost no dialogue!
Oh, and in the final act, the gorilla shark squid appears, too, drawn in by all the blood in the water. Or maybe that's the sequel.