While the British Virgin Islands’ most impressive snorkeling is generally found around outer islands, you should not write Tortola [1] off completely. There are several nice snorkel sites easily accessible from the beach.
The best snorkeling around Tortola is found at Marina Cay, a small island just off the coast of Beef Island [2]. Smuggler’s Cove [3] on the west end has a shallow offshore reef best explored in calm weather. Other good snorkel sites are Gun Point, at the western point of Smuggler’s Cove, and at both the western and eastern points of Brewer’s Bay.
Snorkel equipment can be rented from any of the dive operators listed under Diving. Or try BVI Yacht Charters (Road Town, 284/494-4289) or Cane Garden Bay Pleasure Boats (284/495-9660), which rent mask, snorkel, and fins for about $10 a day.
Links:
[1] http://www.moon.com/destinations/virgin-islands/tortola
[2] http://www.moon.com/destinations/virgin-islands/tortola/sights/beef-island
[3] http://www.moon.com/destinations/virgin-islands/tortola/sights/west-island/smuggler-s-cove