The most outstanding dive site in Mafia Island is Chole Bay. It is a vast circular bay where the depth goes from 5 to 27 mt. Safe dives are possible throughout the whole year in this bay, which is like a natural harbor. Outside Chole Bay world-class dive sites can be found with, among other attractions, 20m+ deep walls in pristine condition and one of the most varied and vibrant sealife gatherings in East Africa.

Mafia Island Diving offers great diving for advanced and novice divers in safety under professional instruction (PADI certificate). The snorkeling on the shallow reefs surrounding the many islands in and around Chole Bay is a great attraction for non-divers and divers alike. Trained diving assistants handle all equipment, help divers and check their equipment, so that you are free to enjoy the dives and all other activities during each day.

Almost all Mafia's best diving is at depths of less than 30m so it is a sport diver's paradise. The reefs of the archipelago offer a staggeringly beautiful and varied display of marine life. The excellent condition and high diversity of the reefs stimulated the creation of Mafia Island Marine Park, Tanzania's first marine park. Examples of most kinds of tropical marine habitat occur here, including exposed fringing reefs, rock walls, and soft coral and algae-dominated reefs. The diversity of animal and plant life is hard to match, with over 48 genera of coral and 400 species of fish so far identified.

Large predatory fish and turtles are common and surprisingly unaffected by approaching divers. Many reef creatures are nocturnal, avoiding daytime predators. As the light fades and the rich "soup" of plankton rises from deeper water, the daytime, rock-like appearance of coral is transformed into a brilliance of colour as the polyps emerge from their stony cups to feed on the plankton. Night diving is focused on the many small, delicate reef species usually missed during the day.