The most fun sequence in Bedknobs and Broomsticks is arguably the Soccer Game between the Dirty Yellows and the True Blues. But the preceding underwater sequence has its moments as well. As usual the live action/animation mix is done extremely well, as you can see in the frame above. Angela Lansbury holding an animated/drawn trophy looks magical. It is always such a pleasure to see live actors interacting with drawn characters in such a way!
Here are a few sheets with design drawings for a variety of fish characters. Milt Kahl's drew some of them, his drawings are sketchier than the ones done by other artists.
Here is the link to an earlier post about the film's soccer game: