Two scuba divers are left behind in shark infested waters, when their tour boat leaves without them. Open Water is based on true events, when two American tourists were left behind on the Great Barrier Reef. Fortunately for Australian tourism, this movie does not take place off the coast of Australia, and the actual incident is not referred to in any detail.

Open Water has the feel of a documentary, probably because it was filmed on such a low budget, in the open ocean, with real, untrained wildlife. Most of the movie is what happens with the couple after the boat has gone. We listen to them talk as they go from disbelief that they could have been left behind, to wondering when they will come back as surely it's been noticed by now that they are missing. We see day turn to night as they remain floating in the water, wondering what is swimming around beneath them. You get a sense of being in the water with them, and so experience some of the same fear when a shark fin appears, and then disappears. Because of the realism this film was scarier than many other films I've seen recently.