Murder Island.

It's summer. A group of teenagers decide to go on a camping trip. They drive far up in the country until they find a small place were they rent canoe's for a cheap price. The group paddle for a long time before they find the perfect island to set up camp on. They have sex, do drugs and drink alcohol. But the next morning they notice that one of them has disappeared. They split up to go looking for her, but that proves to have horrifying consequences...