Where to Watch Doombeach (1989)

A young boy dies after swimming at a seaside resort, and the local children, led by Gavin, investigate and are led to suspect that contamination from a nearby nuclear plant is to blame. Their teacher is sympathetic, but has broken into her house, perhaps as a warning. Gavin is nearly killed after talking about the problem on TV, but gradually all is uncovered - with terrible consequences for Gavin.