Yes, but not on St Thomas! Take the ferry ($6 or 8) over to St John for the day and swim the north beaches. It's beautiful over there!! You can catch a cab/bus for next to nothing from the ferry dock to the nearby beaches too. The beaches are gorgeous and the water is stunning. Here's a link to the map for the B2B race held every Memorial Day weekend that will show you which beaches to swim. www.friendsvinp.org/race-course-map
I guess if you had to go to St Thomas, though, Meghans Bay is probably the best swimming beach. Long and square.
Magen's bay is one of the most beautiful beaches in the world. It used to be listed on various lists (may still be). You'll recognize it because you've seen it in TV commercials. It is U-shaped with trees on either side, but a short beach with palms hanging over the water. An island in the middle at the top of the U would be great to swim out to.
