80's/90's Horror TV Show/Movie Help?

I remember back when I was young staying up late one night with my parents and watching a horror movie or episode of a TV horror show. All I can remember was that a bunch of friends are hanging out by a river and they're out on a raft. Slowly but surely something in the water begins to eat them all, although I'm not entirely sure what it was. It might not have been revealed at all. The thing is I don't know what this was from! I looked up both Tales from the Darkside and Tales from the Crypt synopsis' but there's nothing that matches. It might have been a movie playin on TV. This all happened mid-90's so I think it was either a 80's or 90's project. Any help is greatly appreciated!!