You'd have to be pretty dumb to not know what a No Swimming Sign in Florida could mean. A good Parent would assume worse case scenario. It's fine I can agree there may have been a number of reasons it COULD have been there or interpreted, but seriously there should be #1 reason above all else you could imagine .....
DANGER!!!!
If it's dangerous and the rules say don't do it, do you really need to know why before you agree you "accept" their terms on their property why they are telling you to stay out or off a certain part of THEIR property?
Break my rules of my house, and it will be worse than an angry gator LOL
People would go running to the Gator like "Help...help me Mr Alligator, he's gonna kick my ***"