There's some good coral and fish to see here if you can get to Whistling Cay. It would be tough to get here without a boat of some sort. I got here on a chartered boat and enjoyed the snorkeling, though it wasn't my favorite on the island.
Snorkeling has been better at numerous other St. John locations. Good for first time, inexperienced, beginning snorkelers. Plan your day there carefully as that is where the St. Thomas cruise ships take excursions.
Note that there is a nominal fee, faculties are available as well as lifeguards .