Northeast of Christiansted off St Croix USVI, the snorkeling at Buck Island Reef is popular for the 700 acre fringing coral reef formation and the established underwater snorkeling trail. Buck Island is a national monument where you can follow the underwater trail around the elkhorn coral grottoes and where you might see hawksbill turtles. The underwater Buck Island Reef National Monument snorkeling trail was designed for more experienced snorkelers due to rough surf, and is located on the east side of the 176 acre Buck Island. Among the 250 types of fish, you can expect to see blue tang, parrotfish, spiny Caribbean lobster and barracuda. In reality, the snorkeling trail is quite short, but it gets you to a location that is quite scenic.
While the snorkeling is great off Buck Island year-round, the summers are much less crowded. The Fall and Winter seasons are known to be windy, so the water visibility suffers. Buck Island is a 5.5 mile boat trip from Christiansted Wharf or Green Cay Marina, and worth a full day snorkeling trip. There are five licensed charter boat companies at Christiansted Wharf or Green Cay Marina. If you decide to go for a full day trip, you'll want to check on how much time is actually spent snorkeling at Buck Island -- some of the trips have only the same amount of time as the half day trips.
In addition to the snorkeling trail off the east side of Buck Island, there is good snorkeling off the northwest corner at high tide. There are nurse sharks, lobster and southern stingrays.
Here are some general notes about traveling around St Croix. First, if you plan to be snorkeling at multiple dive sites on St Croix, you will want to have a rental car so that you are not at the mercy of the St Croix Taxi Association. Those taxi costs, especially for multiple people, add up quickly. When renting a car, you will want to make your rental car reservation several months in advance to make sure there is actually one available when you arrive. Multiple reservations might not be a bad idea, but just make sure to cancel the extra reservation when you actually get your car. There are several popular island-only rental car companies, too. Second, do not leave your valuables unattended anywhere due to theft on the island. The hotel safes are known not to be all that safe, either. Carry valuables with you or leave with someone you trust. Third, make sure to arrive on island with low expectations for the beach resorts, especially, the Carambola Beach Resort and the Chenay Bay Beach Resort. Check out the hotel review websites and make your own educated decision.
Overall, Buck Island is the 2nd most popular snorkel dive spot of all 10 snorkeling dives in St Croix.