Mafia Island Marine Park covers 822 square kilometres of reef, lagoon, and open water, and it protects what is generally considered the best diving on the Tanzanian coast. The reefs here have seen less pressure from divers than those around Zanzibar — a significant advantage for coral coverage and fish populations. Expect walls, coral gardens, and channels where current brings in pelagic fish; turtles are common, and the visibility can exceed 30 metres in the right season.
There are no large dive operations or resort instructors offering entry-level courses in industrial quantities. The handful of dive centres operating from the island's lodges are small and typically only take experienced divers on their best sites. If you are a beginner, Mafia is not the right place to learn — the currents can be strong and the conditions variable. For an intermediate or advanced diver willing to accept limited infrastructure, it is one of the best dive destinations in East Africa.