Mopion is about the most photographable thing in the Grenadines: a perfect oval of white coral sand, perhaps thirty metres across, sitting alone in turquoise water with a single palm-thatch umbrella stuck in the middle. There is nothing else — no rock, no tree, no shade except under the umbrella. At high tide the whole sandbar is reduced to a smudge; at low tide you can walk across it dry-shod.
Getting there is the trick. Petit St. Vincent's water-sports staff will run you out by Hobie Cat or motorboat, and most charter yachts cruising the Grenadines stop here for a swim. There is excellent snorkelling on the reef immediately west, with parrotfish and small reef sharks common.