Open Water is a 2003 American survival horror thriller film. 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.

The film is loosely based on the true story of Tom and Eileen Lonergan, who in 1998 went out with a scuba diving group, Outer Edge Dive Company, on the Great Barrier Reef, and were accidentally left behind because the dive-boat crew failed to take an accurate headcount.

The film was financed by the husband and wife team of writer/director Chris Kentis and producer Laura Lau, both avid scuba divers. It cost $120,000 to make and was bought by Lions Gate Entertainment for $2.5 million after its screening at the Sundance Film Festival. Lions Gate spent a further $8 million on distribution and marketing. The film ultimately grossed $55.5 million worldwide (including $30 million from the North American box office alone).

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.