We stayed at Sapphire Beach Condo, St Thomas, USVI in May/June, 2014. We looked for a place where we can walk to beach and snorkel without crossing a road. Being experienced snorkelers, we didn't look for a great reefs or fancy tropical fish. We wanted some reefs that support marine life.
Well, There were more reefs than I expected. Also there were nice grass beds. We thoroughly went through Sapphire Beach (including St. John Bay). We saw many turtles, string rays, some spotted eagle rays on the grass beds in 15-20'of water. Trunk fish, trumpet fish, and other tropical fish were found in 5-20' of water where reefs were formed

We snorkeled everyday whenever we found the a couple of hours between other activities.