I saw this in the 90s when I was a kid, and it was on VHS (but the tape was destroyed so we threw it away). It was in English, and I don’t remember whether it was color or black/white but I’m pretty sure it was color.
The movie was live-action, no animations that I remember.
I remember there was a kid on the beach, looking at a canvas (maybe an old man was painting it?) and he has some dream or actually enters the ocean. He talks to a variety of sea creatures (animatronics or puppets) who talk and sing about how pollution is ruining their ocean. There’s a scene that looks like a little desert under the ocean, with lots of trash on the bottom. I believe the kid helps pick up the trash, and the end of the movie it shows a finished painting with a bunch of different sea creatures on it, and I believe it featured a clam in the bottom, left-hand corner of the painting.