An Indian Ocean archipelago south of Zanzibar protected as Tanzania's first marine park, Mafia Island pairs a rare year-round resident whale shark aggregation off Kilindoni — a surface-snorkel encounter — with sheltered, coral-rich diving inside Chole Bay and dramatic drift and wall dives on the outer reefs during the Kaskazi monsoon.
Conditions, highlights, and the resident marine life.
Water and air temperature across the year.
Mafia Island Marine Park (MIMP), gazetted in 1995 as Tanzania's first marine park, protects roughly 822 km² of reef, mangrove, seagrass and lagoon — more than 75% of it submerged — making it the largest protected marine area in the Indian Ocean and home to over 400 fish species and around 273 species of coral. The island's signature draw is a population of around 200 photo-identified whale sharks (Rhincodon typus) that, uniquely, remain in the deep waters off Kilindoni on the island's western side year-round; acoustic telemetry (Cagua et al. 2015) and a follow-up study (Rohner et al. 2020) showed high year-round residency even though surface sightings peak in the calmer northeast-monsoon months. The aggregation is dominated by juvenile males (around 87.5% male, 4–9 m, median 6 m) feeding on dense patches of sergestid shrimp, and encounters are by snorkel only. Diving is split by monsoon: the well-sheltered Chole Bay — a roughly 50 km² basin reaching 28 m — is diveable in almost any weather and suits all levels, while exposed outer sites such as Kinasi Pass and Dindini Wall, with their stronger tidal currents and pelagics, are best during the Kaskazi (NE) season from October to March. Water is warm year-round (about 25–29°C) and visibility commonly runs 20–30 m outside the April–May rains.
What makes this dive worth the trip.
43 species you’re likely to encounter on a dive here.
7 signature sites at this destination.
The only true vertical rock wall found around Mafia, on the outer reef east of Chole Bay and exposed to open ocean, so it is diveable mainly during the Kaskazi (NE) monsoon from October to March. The wall rises from around 28 m to about 8 m below the surface and is cut with small caverns and overhangs that hold pelagic action. Stronger currents and bigger fish make it one of the island's signature advanced ocean dives.
A roughly 12 m spire of ancient coral rock standing in the inner part of Kinasi Pass, close to the last rock island, with a maximum depth of about 24 m at the base of the spire. The structure concentrates fish life and is known for large potato cod, a resident giant moray eel and giant batfish. Current can pick up given its position in the pass, so it rewards good buoyancy and timing.
Not a scuba site but the shallow western-shore area off the port of Kilindoni where Mafia's resident whale sharks surface-feed on dense sergestid-shrimp patches, encountered by snorkel only. Surveys for the long-term whale shark research project began and ended here, and the aggregation is most reliably seen at the surface during the calmer Kaskazi months (roughly October–March, peaking November–December). Operators run from small boats following a whale shark code of conduct.
A versatile reef inside Chole Bay reaching about 21 m, noted for unusual dome-like Porites coral formations and a good mix of hard and soft corals. Calm conditions and modest current make it a dependable second dive and a strong site for macro and critter hunting, with lionfish, clouds of glassfish, moray eels and frequent nudibranchs, frogfish and octopus. Diveable in almost any weather.
The most celebrated dive in Chole Bay, a tidal channel drift that begins on a deep shelving reef around 20–26 m and rises to a shallower wall at roughly 6–15 m, threaded with small caverns and overhangs. Tidal currents funnel through the pass and draw great shoals of reef fish, barracuda and carangids alongside large groupers, parrotfish and pelagics that come and go with the tide. Best dived on a slack tide or slight incoming current, and considered the bay's most advanced site when the current runs.
A gentle sloping reef wall inside Chole Bay descending to around 15 m, draped in a rich tapestry of hard and soft corals smothered in clouds of small fish. Calm, sheltered conditions make it an excellent introductory dive and one of the bay's better night dives, with damselfish, fusiliers, butterflyfish and angelfish by day and nudibranchs and flatworms turning up in the cracks. A reliable all-conditions site suitable for beginners.
A large, shallow field of densely packed coral bommies set behind the Kinasi and Chole walls inside Chole Bay, with depths of roughly 3–8 m. The coral is exceptionally dense and continuous in places, separated elsewhere by seagrass and sand patches, hosting a high diversity of reef fish and anemones. Shallow, calm and bright, it is ideal for beginners, snorkellers and photography.
Local dive centers, resorts, and hotels.
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