I didn't get the chance when there last year to snorkel the horseshoe area, inside or out. I was however pleasantly surprised by the snorkeling in the area I highlighted in red on the attached image. Depth
there was a fairly steep drop from 5' to 40'.
You can take a mooring
in the sand area east of Petit Rameau in the horseshoe just west of the coral
heads. In light conditions you can take one of the moorings right off of Petit Rameau on it's east side with the beach right on your stern, but it's way too choppy when the wind
The calmest moorings are between the islands right off of the beach where they have the lobster bar-b-que, but it's a high traffic (slow speed, no wake) area and you need to grab one of those moorings early in the morning because they are desirable as you can just swim to/fro the bar-b-que.
Biggest drawback by far is the highly aggressive nature of the all the boat
boys. Absolutely beautiful spot, one of the most beautiful in the world, but don't expect any peace and quiet, or to be left alone. If you bar-b-que with Alphonso, then Romeo will hate you, and vice versa. They are all basically the same and set their tables up next to each other. 6 of one, half dozen of another, IMO.
I loved Salt
Whistle Bay on Mayreau, had a great stay, but when a slight north swell kicked up it became untenable with waves crashing on the beach that made dinghy
landings impossible, so visit in settled weather