re: Fontainebleau State Park questions

Camping- cool, I think.
Swimming- okay. The water at the beach is kinda bleh and some sketchy types group up there, but kids don't seem to give a shite about either.
Fishing- don't know for sure but there are fresh and salt water spots. If you are mobile and go off the beaten path there may even be some really good spots.

Along those lines, there is a cool boardwalk that goes pretty far out into the lake where you can see all kinds of stuff. Kids will love it. Just watch out for any gators.