There are many half-day trips out to Buck Island,and, unless you have your own boat, they are the only way to get there. My goodfriend, Joe Prentice, owns a company whose job it is to book those trips.

Marty is referring to Buck Island off St Thomas.

In order to go to Buck Island off St Croix, you would have to fly over, probably on the seaplane, then take a boat. Pretty time and $$$ intensive. I would save that trip for a time you stay on St Croix and enjoy the snorkeling around St Thomas!

Just for clarification for those reading. There are two Buck Islands.

Buck Island Reef National Monument, off of St. Croix
The Buck Island area was first protected in 1948 and later became a national park in 1962 under the direction of John F. Kennedy. Buck Island National Monument is 6000 feet long and ½ a mile wide. Uninhabited Buck Island is 340 feet above sea level. The National Park Service manages this underwater monument of extraordinary marine beauty. Buck Island offers a pristine white sand beach; excellent snorkeling and a wonderful look at marine life around spectacular coral reefs and gardens. There are several species of coral and almost 90 species of fish in the park's waters. This 880-acre monument created by nature is a mile off the northeast coast of St. Croix. It is made up of 176 acres of land and 704 acres of underwater area. It is one of the most popular attractions on St. Croix. The crystal clear water and beautiful underwater scenery at Buck Island is legendary. With a mask and snorkel you will be treated to some of the most fabulous underwater views in the Caribbean. This ecological site may take the whole day to explore. There are hiking trails on the island that are worth visiting and underwater trails to follow while snorkeling. Several species of turtles and birds nest in the area. Two thirds of the island is surrounded by an Elkhorn coral reef and coral gardens. The water is teaming with hundreds of colorful tropical fish. Without question Buck Island is a must see.

And...

Buck Island National Wildlife Refuge, off of St. Thomas
Established: 1969. Acres: 45.
Location: the island is located 2 miles from the south coast of St. Thomas. Administered under Caribbean Islands NWR office.
The island was transferred to the Fish and Wildlife Service due to “its value for migratory birds.” Although the rocky coastline offers little in the way of recreation potential, the surrounding waters contain reefs and a shipwreck that attract large numbers of snorkelers, divers, and boaters. The Coast Guard maintains a lighthouse on the refuge.

Hello Steve,

As East Ender mentioned you'd have to take the Seaplane or Cape Air or another small airline over to St. Croix. ($85-$120 rough estimate roundtrip, per person).

And then once on St. Croix you could take a charter out to Buck Island like this one http://www.bigbeards.com/

The seaplane lands in Christiansted so you can then walk over to Bigbeards or the other charter boat offices which are right in the shopping area in Christiansted. If you are going over for this I would definitely make reservations, just letting you know the offices are convenient to the Seaplane. The small airlines would go from/to the airport, so you’d need to take a taxi to the charter boat office/meeting point.

Perhaps plan on overnighting on St. Croix, if you are interested in any other sites over there.

There aren't any charter boat trips from St. Thomas to St. Croix/Buck Island and the ferry between St. Thomas and St. Croix only runs during season (December-May).

--Islander