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 kilometres in extent. These reefs have been declared a Marine Conservation area.