Mayotte's lagoon contains some of the finest diving in the Indian Ocean. The barrier reef shelters an inner lagoon with calm, clear water, and the reef itself drops away into oceanic depths on the outer face, providing wall dives and encounters with large pelagic species — hammerhead sharks, manta rays, whale sharks in season. Dive sites include the famous Passe en S, a winding channel through the reef where currents concentrate fish in spectacular density.
For snorkelers, the beaches at N'Gouja, Bouéni, and Saziley offer easy access to reefs where sea turtles are so numerous that close encounters are almost guaranteed. Several dive schools operate on both Grande-Terre and Petite-Terre, offering guided dives and PADI certification courses. The water temperature stays between 25°C and 29°C year-round.