You can rent water mice & other boats. WDW has a lenght of stay plan where you can rent boats & bikes for abt $200. If you think they will be renting the boats a bit, you may want to look into it. The water mice are fun. My dh loves them.
They do have parasailing. I think it books pretty fast. I think you call that 800-play number (don't remember the full #, but I'm sure it's on their web site.) If I remember right, the parasailing starts at abt $125.
No swiming on the lake anywhere. Alligators & bacteria.