Continuity mistake: When Rennie and Sean are on the ladder in the sewer Rennie's position changes between shots. (01:29:50)
Continuity mistake: When Toby turns up at the end, in the street, in the first shot of him his shadow is short. In the next shot it's very long. (01:32:15)
Continuity mistake: Jason's shown as being a regular faced boy of 8 or 9 when he drowned. This is inaccurate as the original Friday the 13th showed he was deformed as a child.
Continuity mistake: In part 7, Tina uses her powers to split the hockey mask in two. In some shots you can see the straps of the mask cut into the back of Jason's head, leaving large cut marks. However in this movie when the mask is removed, the cut marks are not there.
Continuity mistake: Not long into the movie, Reni is looking for her dog. Next time we see the dog, it is on her lap in the life boat. Between these two scenes they never show her finding the dog: it just appeared out of nowhere.
Continuity mistake: Somehow Jason acquires a pair of gloves he didn't have in Part 7: The New Blood.
Continuity mistake: The previous movie saw Jason looking dark greyish brown, here he's a slimy light grey and has gained a pair of black rubber looking gloves.
Continuity mistake: Rennie's visions of Jason as a boy change their appearance constantly throughout the film. At some points he is bald and deformed, much like how he was in the original film. At other times he appears as a normal, non-deformed boy with a full head of brown hair. At some moments he even appears as a mix of both (with a deformed face, but a full head of hair). This inconsistency is never explained or even acknowledged.
Continuity mistake: When Jason is holding Eva in the air, he lifts her up higher towards the ceiling, but in the shots of her feet, they stay in the same position.
Continuity mistake: Crystal Lake goes from a lake surrounded by land in previous installments to suddenly having the space for a small yacht and a channel that feeds right to the open ocean.
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