As far as I can remember there was a young boy who rode his bike to a lake nearby where there's once of those metal structure windmills that creaks - the place I think is abandoned. There's some mystery - a "thing" in the water that comes to the surface. I think he goes back without his friends to investigate further and goes missing. His friend goes into his bedroom and sees a treasure chest or JCB in his fishtank and sees how it opens to release air and realises that's what's in the lake and where his friend is. I know it's vague, I've no idea of the title or actors - it would have been 20 odd years ago I saw it and remember loving it as a child. Would really love it if someone can help!

Frog Dreaming (http://www.imdb.com/title/tt0091810/) aka The Quest.

Hello, Thanks for that - have just found it on someone else's questions - can't believe I finally know after all these years! Thanks again!