Beneath (2013)

After six teens graduate from high school, they decide to spend one final outing with each other on a rowboat in a lake before they go their separate ways. However, after a man-eating fish kills one of them and destroys their oars, they find themselves trapped in the middle of the lake. Soon afterwards, they realize they have to determine who is to be thrown into the water as a distraction, so the rest of the group can paddle to shore.