The Lake Eyre basin (/ɛər/ AIR) is a drainage basin that covers just under one-sixth of all Australia. It is the largest endorheic basin in Australia and amongst the largest in the world, covering about 1,200,000 square kilometres (463,323 sq mi), including much of inland Queensland, large portions of South Australia and the Northern Territory, and a part of western New South Wales. The basin is also one of the largest, least-developed arid-zone basins with a high degree of variability anywhere. It supports only about 60,000 people and has no major irrigation, diversions, or flood-plain developments. Low-density grazing that sustains a large amount of wildlife is the major land use, occupying 82% of the total land within the basin. The Lake Eyre basin of precipitation (rain water) to a great extent geographically overlaps the Great Artesian Basin underneath.
The basin began as a sinking landmass mostly covered by forest and contained many more lakes than now. The climate has changed from wet to arid over the last 60 million years. Most of the rivers in the Lake Eyre basin are now slow flowing, flat, and completely dry for lengthy periods. When the country north of the basin floods, floodwaters drain via the main rivers of the basin—Cooper Creek, Georgina River, and Diamantina River—southwards towards Kati Thanda–Lake Eyre, the country's lowest point at 16 metres (52 ft) below sea level. The water overflows the river banks, across the floodplains, filling waterholes and wetlands and carving new channels, giving rise to the name Channel Country. Most of the rain which falls in the north never reaches the lake 1,000 km away, which only fills occasionally.