Audio problem: When Jim says "Gotta throw the anchor over" his mouth is slow and out of sync. (00:04:25)
Audio problem: When J.J. is jammin' to her song she notices Jason and screams. She then runs away, and magically the song that was playing on her tape player has stopped. (00:21:15)
Chosen answer: To the best of my knowledge, this is just a bit of a continuity mistake. While previous films have not indicated Crystal Lake is connected to the ocean, this film portrays it as being connected. You just kinda gotta go with it for the movie to work.
TedStixon