Do you have a specific reason that he needs to know? Unless it causes trouble for either of you or your team (if you're on one), I'm not clear on why you'd like to tell him.

It's hard to comment on whether it's a good idea without any context, but my initial reaction without knowing anything is to say you should keep it to yourself. If you're having specific swimming-related difficulties that you need accommodations for, then that would be a reason to tell him-- and to ask for those accommodations of course.