Another vague one, I’m sorry!

I remember one scene only – of a boy diving to retrieve something from a spacecraft which is underwater. He may have entered through the roof, or possibly through a damaged section. He may have had a large conch shell or similar.

I don’t recall if the boy was human or actually alien masquerading as human but I’m inclined to think the latter.

I don’t think it’s Flight Of The Navigator (since the craft there is captured) or either of the Cocoon films.

This was shown on TV so may have been an episode of something, but ISTR it being a movie. I also remember it being in colour but it could have been B&W with colour added later.

The only details I remember was the use of what I think were cardboard cut-outs for humans transformed (drained? sucked dry?) by some alien influence, and the presence of some small black objects (small rocks? football sized or a little bigger) littering the area (desert/scrub IIRC, maybe South West US states).

It’s not Monolith Monsters or It Came From Outer Space as I’ve checked both.