Snorkeling is probably the most popular activity on St. John , and for good reason. It requires minimal equipment and allows you to explore the underwater cornucopia of fish, coral, shellfish, turtles, and other marine creatures that live in the waters around St. John. Because of strict rules governing fishing, anchoring, and pollution in national park waters, the snorkeling around St. John is excellent.
You can snorkel anywhere. Most people gravitate toward coral reefs, but snorkeling over sea grass or in the mangroves can be just as interesting. The National Park Service publishes a brochure, Where’s the Best Snorkeling?, that gives detailed descriptions of snorkeling at the major beaches on St. John.
On the north shore, the Trunk Bay Underwater Trail  is a good reef for beginners. Signs along the sea floor identify types of coral and fish, and lifeguards are on duty for safety. Jumbie Beach  has a shallow, maze-like reef along the eastern (right-hand) side, where you may see lobsters and nurse sharks. Waterlemon Cay , accessible via Leinster Bay, has excellent coral reef snorkeling.
When the north shore is too rough for snorkeling, try south shore bays, which are normally calm. On the south shore, Salt Pond Bay  has good reef snorkeling around the two jagged rocks that break the surface of the bay. There is also good snorkeling on the eastern shoreline (nearest Ram’s Head ), which gets better the farther out you go. At Great Lameshur Bay , the snorkeling is best along the eastern shore. You may see the sunken foundation remains of Tektite, an underwater habitat for aquanauts from 1969 to 1970. Little Lameshur Bay  has snorkeling for beginners just off the western end of the beach. If it is calm, strong swimmers can explore the western shoreline, which features deep cliffs, canyons, and schools of fish.
Maho Bay  has offshore sea grass beds that provide food for green turtles, especially in the early morning and late afternoon. Leinster Bay  near Annaberg on the extreme northwestern end of the island has nice sea grass beds, where you may see sea stars, conch, and turtles. Brown Bay, accessible only on foot, has a sea grass bed just offshore. Although not part of the national park, Chocolate Hole has a thick sea grass bed where you can see juvenile fish, rays, conch, and sometimes turtles. Chocolate Hole was named for the color of the rocks along the shore. It is located on Route 104, on the southern coast.
Mangroves are not as flashy as reefs or sea grass, but they provide a fascinating glimpse into an important marine habitat. Mangroves are where juvenile fish, lobsters, and crabs live until they get big enough to fend for themselves in the great big ocean. Mangroves are often referred to as the nursery of the ocean. The best place for mangrove snorkeling is Princess Bay along Route 10 (East End Road). Get as close to the knobby trees as you can, and look carefully for the marine life. It is shallow, and fins will disturb the sea bottom; it is best not to wear them.
If snorkeling appeals to you at all, it is a good idea to rent snorkel gear for the duration of your stay. It is cheaper than renting it by the day or hour, and that way you will always have gear on hand. Check first to see if where you are staying has or rents snorkel equipment; most hotels do. You can also rent snorkel gear from any water sports operation on the island.
In Coral Bay , Crabby’s Watersports (Coccoloba Shopping Center, 340/714-2415) rents a full set of snorkel gear for $10 a day or $50 a week. Near Salt Pond Bay , Estate Concordia (Concordia, 340/693-5855, 8 a.m.–7:30 p.m. daily) rents gear for $8 per day.
In Cruz Bay , Low Key Watersports (Wharfside Village, 340/693-8999) rents gear for $7 a day and $35 a week. Water sports shops at Trunk Bay , Cinnamon Bay , and Little Maho Bay  also rent gear.