Diamantina River, intermittent river, east-central Australia, in the pastoral Channel Country. It rises in Kirbys Range, northwest of Longreach, Queen., and flows (seasonally) for 560 miles (900 km) southwest past Birdsville to Goyder Lagoon in South Australia, draining a basin of 61,000 square miles (158,000 square km). In times of flood, the Diamantina River and the Georgina River (from the north) merge to drain along the channel of Warburton Creek southwestward to Lake Eyre. The Diamantina’s principal tributaries are the Western and Mayne rivers. The Diamantina’s average annual discharge at Birdsville is 890 cubic feet (25 cubic m) per second, ranging from 50,000 cubic feet (1,400 cubic m) per second in flood to nothing in dry years.