The sharks used in this film were Caribbean Reef Sharks. The cast wore chain mesh under their diving suits for protection and though none of them was bitten by the sharks, Blanchard Ryan (Susan) was nipped by a barracuda on the first day of filming. In the movie, after Susan is bitten, her boyfriend says, "It was probably a barracuda seeing what you taste like."
Blanchard Ryan is in fact deeply afraid of sharks and as a result Daniel Travis had to enter the shark infested waters first each day to assure her they were not in danger.
The actors were tethered to the boat so they did not drift off into the strong currents.
This movie was financed by director Chris Kentis and his wife, producer Laura Lau, both avid scuba divers. The movie cost $130,000 to make and was later bought by Lion's Gate for $2.5 million after its screening at Sundance.