I've had this movie on my mind for a long time now.
It is about a group of teenagers going to a lake for a day off. They embark on a floating wood deck and they let themselves float free over the lake.
Suddenly they start to see a sort of "mud puddle". This thing is getting closer to them and suddenly tries to reach for them through the crack on the wood deck, it even manages to make some of the teenagers to fall and the "mud puddle" kinda swallows them.
It ends with one of the teenagers finally capable of reaching the shore, but she or he crawls too slow and the "mud puddle" manages to get its last victim. and then the movie or episode comes to a silent end with the sound of the flapping water.
If anyone could help me here I've seen this on TV in the mid 90s.
Thanks for any information.