Director Alexandre Aja planned to have Joe Dante (director of the original Piranha (1978)) and James Cameron (director of Piranha II: The Spawning (1982)) play boat Captains who give safety lessons to the teens. Dante wanted to do it, but Cameron was too busy.
Kelly Brook and Riley Steele spent two weeks training for their nude synchronized underwater swimming set piece.
A television spot was banned because it had too much gore, and it also revealed the ending to the movie.
Kelly Brook auditioned with an American accent. This deeply disappointed Alexandre Aja, who called her back and asked her to speak in her natural English accent. He felt the character would be much more appealing if Brook played her in her normal voice.
The production crew estimated that seventy-five thousand gallons of fake blood were used each day.
Richard Dreyfuss: The Jaws (1975) star appears as fisherman Matt Boyd at the start of the film. Dreyfuss donated his entire $50,000 salary to charity. Boyd is dressed like Hooper, the character Dreyfuss played in Steven Spielberg's movie.
Ashlynn Brooke, Gianna Michaels: The adult film actresses play victims. Michaels plays the parasailing girl. Brooke plays the member of the cheerleading team, who is cut in half by the loose steel cable.