We've stayed there 3 times I think, it is our preferred spot in Marathon. The best sites are the waterfront ones and they charge extra for them. The 'waterfront' is on their concrete wall around their little bay. They have a marina you can dock your boat at if you have one. Swimming and snorkeling right there in their little bay with small white sand beaches. There are actually things to look at if you snorkel. One thing to know, if there is an onshore wind it will stir up the sediment and reduce visibility to zilch.
Not a fancy resort style park but it has what you need and is cheaper than the ones with a bunch of extras that we will never use anyway.
Do check out the many snorkel/diving boats that run trips out to the reefs. Very much worth the trip(s), not pricey either. They will supply all the gear if you don't have your own.
Arctic Fox 25Y Travel Trailer
2018 RAM 2500 6.7L 4WD shortbed
Straightline dual cam hitch
400W Solar with Victron controller
Superbumper