Horror With Kids and a Camero

by Werdna
(Texas)

There is a Horror movie from the 80's, I think, that I need to find. I can only describe parts that I remember:

There are some kids who go to a lake in a Camaro (the classic Camaro from 80's), maybe 3 or 4 kids. They go swimming in the lake and swim out to this platform in the lake. They get stuck on this platform because the "algae" in the water kills them if they get in it...

That is the best I can remember. Any ideas?