Many people would like to snorkel or dive when they come here, and you can, but it is a different kind of snorkeling. There are no coral reefs off Key Biscayne that you can reach safely from the beach – they are too far out to swim to and located in the boating zone which could be a huge problem unless you come with a dive flag and buoy. If you are a good swimmer, there are some rocks with nice fish near the lighthouse, but you need to take in consideration the tide and waves. The safe snorkeling or diving will let you see seahorses in the grass, parrot fish, baby queen conch, spotted rays and all sorts of juvenile fish.
One important thing to point out about this beach is that there is no lifeguard on duty, it is swim at your own risk. You need to be mindful of the Beach Warning Flags posted by the ranger station at the entrance for any possible alerts.
More info about the state park you’ll find in this post. Enjoy!