Attack of the Killer Manatee (1997)

Teens on a camping trip find the old road to a boat ramp has been mysteriously removed. They trek through the woods until they find where the road picks up again. When they get to the end of the line they find a nuclear power plant now stands in the once pristine wetlands. They boat out to their island campsite. Strange and mysterious things begin to happen as one by one the teens meet their fate.