SCUBA is out anyway unless you arrange a private boat to get you there. The ferry won't carry it. Doesn't matter anyway, there really isn't any diving close enough to swim to anyway. The marketing hype doesn't really exist, because no one is running snorkeling trips.
All that aside, the corals are extremely fine at the South and North coaling dock. You should run into Nurse Sharks, Goliath Grouper, lionfish, tarpon, and a whole host of tropicals. If you are lucky, you will run into the crocodile (the very lonely crocodile) that lives in the moat, but leaves now and again to go fishing. The coral reef on the North side is spectacular, with staghorn and lots of stony corals, but a bit sparse when it comes to octocorals.
Have fun.
WDA7434