This seems to be a relatively new concept, but some animals are able to benefit from something called hydrotherapy. Essentially it's putting the animal into a pool, where a person holds them up as they swim around. Supposedly it helps strength the limbs and allows animals with walking problems to move around better on land.
Here's a recent story of a cat going through hydrotherapy:
http://today.msnbc.msn.com/id/38328044/ ... d_animals/That's probably pretty rare; most cats I've seen tend to hate the idea of getting into that much water. Has anyone heard of this being used by someone you know?