one of the largest rivers of the island of New Guinea, flowing almost wholly through Papua New Guinea. For a short stretch of its middle course, it forms the border between Papua New Guinea on the east and the Indonesian half of the island on the west. Rising on the Star, Kaban, and Hindenburg ranges of the Victor Emanuel Range in the central highlands, the Fly—fed by its principal tributaries, the Strickland, Alice (Tedi), and Palmer rivers—flows south and southeast for more than 700 miles (1,100 km) to the Gulf of Papua (Papua, Gulf of), Coral Sea, and drains an area of some 27,000 square miles (69,900 square km). The river was named by F.P. Blackwood, captain of the ship HMS Fly, who explored the estuary in 1842. Traversing deep gorges through rainforests in its upper course, the river broadens and deepens its channel below the Palmer Junction. From this junction to the sea, a distance of some 530 miles (850 km), the river is navigable in all seasons for boats drawing less than 8 feet (2.4 metres) of water. This lowest stretch, in which the stream falls only about 50 feet (15 metres), is bordered by open savanna-like country and swampy plains with numerous lakes. The Fly may be in flood from October to April, moving millions of tons of sediment downstream to be deposited as shifting sandbars and islands (Kiwai, Wabuda, Purutu) in its 40-mile- (64-km-) wide mouth. The material, together with that transported by the Digul and other neighbouring streams, has built up an enormous plain bordering the Torres Strait. There are few settlements of any size along the river, but a port at the town of Kiunga, some 490 miles (790 km) inland, ships copper and gold mined in the Star Mountains. Environmental degradation along the upper course of the river system caused by the mining activity has been a source of political tension in the area. There are only a few coconut plantations in the area; crocodiles are hunted. The total indigenous population is scanty.