Beneath (2013)

Six graduating seniors decide to commemorate their rite of passage by partying on an isolated island surrounded by a secluded lake, but the fireworks and alcohol they bring along have nothing to do with the night?s festivities. A legendary creature of the lake soon breaks up the fun by attacking the group and mortally wounding one of them. The teens must now come to terms with the death of a friend and the threat on their own lives. Dealing with certain death in the water and the chaos that ensues on the boat out of hell means double trouble for those just trying to survive the night.