The best place on St. Thomas  for snorkeling is Coki Beach . A healthy fringing reef runs parallel to the beach, with a narrow sandbar in the middle. Gear plus orientation, if you want it, is available from Coki Beach Dive Club (340/775-4220), located on the road to Coki Beach.
You can also snorkel around Cas Cay and the other islands near St. Thomas’s east end. You will need a boat to get to these sites, however—or sign up for a kayak tour of the area.
St. Thomas  specializes in snorkeling substitutes, activities that let you explore the underwater world with more ease and comfort than normal snorkeling. Purists look down their noses at these activities—after all, snorkeling is really quite easy. But for families, people not in optimal health, or folks who want to be able to fit some underwater sightseeing into a busy day of shopping, touring, and dining, these activities make sense.
In Sea Trekkin’ (Coral World Underwater Observatory , 340/775-1555) you put on your swimsuit and a special helmet that keeps you supplied with oxygen and then descend about 30 feet to walk amid the coral reef.
Bob Underwater Adventures (Port of Sale Mall, Havensight, 340/715-0348, www.bobusvi.com ) puts you on an underwater scooter to explore in water about 7–10 feet deep. Your hair even stays dry, and you can wear glasses or contacts without a problem.
The Atlantis Submarine (Havensight, 340/776-5650, www.atlantisadventures.com , $76 adults, $38 children) offers 50-minute underwater tours of reefs around St. Thomas  aboard the Atlantis 15 submarine. The narrated tours go out to Buck Island off the southeast shore of St. Thomas.