The story concerns an American couple who go scuba diving while on vacation, only to find themselves stranded miles from shore in shark-filled waters when the crew of their boat accidentally leaves them behind.

[1][2] The film was financed by the husband and wife team of writer/director Chris Kentis and producer Laura Lau, both avid scuba divers.

[3] It cost $120,000[citation needed] to make and was bought by Lions Gate Entertainment for $2.5 million after its screening at the Sundance Film Festival.

[5] Before filming began, the Lonergans' experience was re-created for an episode of ABC's 20/20, and the segment was repeated after the release of Open Water.

Clips from the film were also featured on NBC in "Troubled Waters", a Dateline episode (July 7, 2008) with Matt Lauer interviewing two professional divers, Richard Neely and Ally Dalton, who were left adrift at the Great Barrier Reef by a dive boat on May 21, 2008.

The next morning, Daniel and Susan's belongings are finally noticed on the boat by a crew member, and he realizes that they must have been left at the dive site.

Sometime later, a fishing crew cuts open a newly caught shark's stomach, finding a diving camera (apparently that of Daniel and Susan).

[7][8] During the audition, Chris Kentis and Laura Lau made it clear to Blanchard Ryan and Daniel Travis that they would work with real sharks in the film and that it was non-negotiable.

Writing in the Chicago Sun-Times, Roger Ebert praised the film highly: "Rarely, but sometimes, a movie can have an actual physical effect on you.

[12] In a much less favorable review, A. O. Scott in The New York Times lamented that it "succeeds in mobilizing the audience's dread, but it fails to make us care as much as we should about the fate of its heroes".