Sponge life, black coral (the finest in the West Indies), and steep drop-offs near the shoreline make St. Croix a snorkeling and diving paradise. The island is home to the largest living reef in the Caribbean, including the fabled north-shore wall that begins in 25 to 30 feet of water and drops to 13,200 feet, sometimes straight down. The St. Croix Water Sports Center (tel. 340/773-7060; www.caribbeandays.com) rents snorkeling equipment for $20 a day, if your hotel doesn't supply it.

Buck Island is a major scuba-diving site, with a visibility of some 100 feet. It also has an underwater snorkeling trail. Practically all outfitters on St. Croix offer scuba and snorkeling tours to Buck Island.

Other favorite dive sites include the historic Salt River Canyon (northwest of Christiansted at Salt River Bay), for advanced divers. Submerged canyon walls are covered with purple tube sponges, deepwater gorgonians, and black coral saplings. You'll see schools of yellowtail snapper, turtles, and spotted eagle rays. We also like the gorgeous coral gardens of Scotch Banks (north of Christiansted) and Eagle Ray (also north of Christiansted), the latter so named because of the rays that cruise along the wall there. Cane Bay is known for its coral canyons.

Frederiksted Pier, near the historic area of Frederiksted, is the jumping-off point (literally) for a scuba voyage into a world of sponges, banded shrimp, plume worms, sea horses, and other creatures.

Davis Bay is the site of the 12,000-foot-deep Puerto Rico Trench. Northstar Reef, at the east end of Davis Bay, is a spectacular wall dive, recommended for intermediate or experienced divers only. The wall here is covered with stunning brain corals and staghorn thickets. At some 50 feet down, a sandy shelf leads to a cave where giant green moray eels hang out.

At Butler Bay, to the north of Frederiksted on the west shore, there are the submerged ruins of three ships: the Suffolk Maid, the Northwind, and the Rosaomaira, the latter sitting in 100 feet of water. These wrecks form the major part of an artificial reef system that also contains abandoned trucks and cars. This site is recommended for intermediate or experienced divers.

Anchor Dive Center, Salt River National Park (tel. 800/532-3483 in the U.S., or 340/778-1522; www.anchordivestcroix.com), is located within the most popular dive destination in St. Croix: Salt River National Park. It operates three boats and dives mainly in and around the park. The staff offers complete instruction, from resort courses through full certification, as well as night dives. A resort course is $90, with a two-tank dive going for $90. Dive packages begin at $250 for six dives.

Another recommended outfitter is the Cane Bay Dive Shop (tel. 800/338-3843 or 340/773-9913; www.canebayscuba.com), with five locations all around the island. The numerous locations means there's a variety of dive sites to choose from, without having to take a long boat ride. A beginner's lesson goes for $60, and packages go all the way up the scale to a six-tank dive package for $199.

Sustainable Diving & Snorkeling -- Touching any coral -- including soft corals such as sea fans -- is forbidden in any marine protected area and should be avoided at all costs everywhere. Even the lightest contact is deadly to the coral and can scrape and cut you as well, leaving rashes and stings much like that of a jellyfish (coral's free-floating cousin). Divers and snorkelers are also not permitted to touch, pet, or otherwise harass any fish, including eels and rays, whose delicate skin is coated with antibacterial slime, which protects them from potentially deadly skin infections.

Feeding fish is similarly dangerous, however innocuous it seems. It can alter natural feeding behavior or, worse, cause the fish to sicken or die from ingesting unfamiliar food.

But wait, there's more: By applying sunscreen or insect repellent before entering the water, divers release harmful chemicals to the water that can mimic the coral's hormones, causing premature death and illness.

It seems the more scientists learn, the more delicate these systems appear. Want to make up for past infractions? Check out REEF (Reef Environmental Education Foundation; www.reef.org), a volunteer monitoring program that allows divers to log in and add their fish sightings to a global database used by scientists to monitor populations.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.