East of Red Hook on the east end of St Thomas USVI, the snorkeling in the Grand Bay (aka Turtle Cove) is a very popular tour destination for a chance to hang with green sea turtles. You'll want to call ahead to see if the turtles are around. Otherwise, there really isn't much to see in these sandy, grass flats in shallow off shore water.
The Turtle Cove snorkeling is located in Great Bay just offshore from the Ritz Carlton Club. Just stay to the right heading out from the main beach. Overall, the visibility is pretty limited and there's not much marine life.
To reach the snorkeling at Great Bay from Red Hook, head south on SR32 (Red Hook Road) for about 0.5 miles. Turn left on SR322 to the Ritz Carlton. To reach the snorkeling on St Thomas by air, fly into Cyril E King Airport (STT) which is located on the west side of the Charlotte Amalie port city. There are direct flights from Miami, NYC, Houston, San Francisco and San Juan, Puerto Rico. In addition, there are inter-island flights from neighboring Caribbean islands, such as from Cape Air. Alternately, there are regular ferry services from Charlotte Amalie to nearby islands of St John, Virgin Gorda (BVI) and Tortola (BVI). The best snorkeling on St Thomas is during the months of May through July when the surf is most calm and the visibility is highest. In case you are in need of a snorkeling tour or snorkel gear, you can check out one of these dive shops including Red Hook Dive Center, Coki Dive Center or Admiralty Dive Center.
Overall, Great Bay is the 5th most popular snorkel dive spot of all 8 snorkeling dives in St Thomas.