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 (1,640 ft) in diameter and about 1.5 kilometres (0.9 mi) in circumference. It is surrounded by an oval reef seven by four kilometre 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.