Real movie turn into cartoon


Hi Movie Forum experts,

I don't remember much about this kids movie(I think it is), but I hope you can help me anyway.

The movie starts out with real persons and the main character is a poor boy. Then he either fall or is pushed into a lake or the sea.
While he struggle under water the movie turn into a cartoon. From then on he can breath under water and get himself into some kind of adventure where he talk to fishes(I think, since I mostly recall the start and the part where it goes from live action to cartoon). I do think it goes back to live action in the end of the movie. I'm not sure, but I think it's from the 80s.

Hope that's enough to find the title of this movie.

Thanks in advance.

Jesper K. (Denmark)

That looks like it. I can see that my memory was a bit of in two things. 1 - it's longer into the movie where he turn into cartoon than I remember. 2 - I remembered that the cartoon was a bit more realistic, but my memory must have refined that part over time.