The Reeds (2009)

A group of friends go away for the weekend but the boat they've rented is unavailable. After a brief argument, they are offered a boat at a different location. When they arrive they find a group of surly teens sprawled all over the deck. After some awkward moments where the teens ignore repeated requests to vacate the boat, the teens leave.

The friends plan to visit a pub after the first day of boating, but the old map they brought makes it impossible to decipher why way to go through the reeds. When they spot a boat in a parallel channel, they decide to follow it hoping it is going to port for the night.

The passageway gradually narrows until it is slightly wider than the boat making travel very difficult. As night falls, an underwater obstruction pierces the boats hull and skewers one of the passengers. As their cell phones can't get a signal, one of the group sees a fire in the distance and heads off on foot in hope of getting help. Turns out the fire is attended by the same teens who were on their boat. It's all down hill from there as there is something or someone in the reeds with a lust for blood.

While the atmosphere is effective for most of the movie, the ending is unclear. Is it a time loop? What is up with the black eyes? How does one guy see himself in the reeds?Will no one notice that five friends who went to rent a boat haven't returned? There's a big difference between a bunch of teenagers who disappear and no one knows where they were going, and a group of adults who disappear on a boating trip. Also how could you not recognize your girlfriend even if she had been burned since she is wearing the same clothes as when you left her?