The Water Babies
When a 12-year-old chimney sweep is wrongfully blamed for being a thief, he makes a run for it, he jumps into a violent river. There he encounters a civilization of anthropomorphic underwater creatures. Before he can return to the surface and clear his name, however, he must help rescue his new friends, the Water Babies, from their nemesis. Featured voices include those of James Mason, Bernard Cribbins and Tommy Pender.
The movie is similar to the book by the same name, although added is a whole new subplot, involving a Killer Shark and the mythical Kraken, who decides whether or not Tom can return to the surface.
There are also several invented characters, which Tom befriends on his quest- Jock, a Scottish lobster, Terence, an effeminate, starstruck Seahorse, and Claude, a foppish French swordfish. Below the "surface of the ocean" is animated, and above is live action.