Just when you thought it was safe to go back into the water . . . “Baywatch” star David Hasselhoff has joined the cast of Bob and Harvey Weinstein‘s schlock horror film “Piranha 3DD.” We are told the Hoff will have his own encounter with the flesh-eating fish in the movie, the sequel of a remake of a 1978 film, “Piranha.” We’re not sure what the “DD” stands for. Hasselhoff joins Ving Rhames, Christopher Lloyd, Gary Busey and David Koechner in the B-picture, due out Nov. 23.