Gau is an island belonging to Fiji's Lomaiviti Archipelago. Located at 18.00° S and 179.30 °E, it covers an area of 136.1 square kilometers, with a total shoreline of 66.3 kilometers, making it the 5th largest island in the Fijian archipelago. Its maximum altitude is 738 meters. It has one airstrip at Lovu at the southern tip of the island, which receives planes from Nausori International Airport.
A marine research facility was established on Naviavia beach on the western coast of Gau in 2005 by UK based NGO Frontier, commissioned by Dr. Joeli Veitayaki of the University of South Pacific, a native of Malawai on the eastern coast.
Rugby sevens legend and player-coach of the Fijian national Sevens Team Waisale Serevi is a native of Qarani, a large village to the north-west, which also contains a post office and nursing station.