Adam & Evil (2004)

After their high-school graduation, eight friends decide to celebrate in a campground in Lake Nede with booze and sex. They get lost and stop in a bar to ask for directions. One of the boys is seduced by the slut wife of the local sheriff, while the group is chased by two bad elements from their school. Once in the lake, one by one is killed by a murderer, and the survivors guess who might be the criminal.