If you get lucky, there might be a manatee that wanders in during swimming season. The rangers just tell you to keep your distance.
If you are really lucky, you might be there when Seaworld releases manatees. One time me and a few buddies where up at the boil, and we were surprised to see two manatees. The rangers said they were used to human contact (probably not a good thing), and not to startle them or try to scare them. They would often swim with you brush up against you.