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."
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.
The school of jellyfish featured in the movie happened to show up on the day the crew planned to film that particular scene. Coincidentally, after that day, no jellyfish ever appeared on location for the whole duration of the shoot.