Mnemba Island is a single small island located about 3 km off the northeast coast of Unguja, the largest island of the Zanzibar Archipelago, Tanzania, opposite Muyuni Beach. It is roughly triangular in shape, about 500 metres in diameter and about 1.5 kilometres in circumference. It is surrounded by an oval reef seven by four kilometres in extent. These reefs have been declared a Marine Conservation area. Mnemba Island and its reef are sometimes called Mnemba Atoll which is incorrect because an atoll is an island that encircles a lagoon, which is not the case for Mnemba Island.
Mnemba Island is a popular scuba diving site, with a wide variety of corals and associated species, as well as occasional sightings of larger species such as turtles and dolphins. Calm conditions are most frequent in November and March, with maximum visibility.
Coordinates -5°48'57.913" N 39°22'56.237" E