Murray–Darling river system

Murray–Darling basin
Drainage basin
An aerial view of the Darling River near Menindee in the far west of the Basin, in New South Wales
Country	Australia
States and territories	Queensland, New South Wales, Victoria, South Australia, Australian Capital Territory
Rivers	Murray, Darling, Warrego, Murrumbidgee, Lachlan, Goulburn, Campaspe, Mitta Mitta, Loddon, and numerous others
Source	Great Dividing Range
- location	Queensland, New South Wales, Australian Capital Territory, Victoria
Mouth	Southern Ocean
- location	Murray Mouth, South Australia
- coordinates	35°35′S 138°53′E / 35.583°S 138.883°E / -35.583; 138.883Coordinates: 35°35′S 138°53′E / 35.583°S 138.883°E / -35.583; 138.883
Length	3,375 km (2,097 mi), NE-SW
Discharge
- average	767 m3/s (27,086 cu ft/s)
Founded	1993
Management	Murray–Darling Basin Authority
Map of the Murray–Darling basin
Website: mdba.gov.au

The Murray–Darling basin is a large geographical area in the interior of southeastern Australia. Its name is derived from its two major rivers, the Murray River and the Darling River. The basin, which drains around one-seventh of the Australian land mass, is one of the most significant agricultural areas in Australia. It spans most of the states of New South Wales, Victoria, and the Australian Capital Territory, and parts of the states of Queensland (lower third) and South Australia (southeastern corner). The basin is 3,375 kilometres (2,097 mi) in length, with the Murray River being 2,508 km (1,558 mi) long.

Most of the 1,061,469 km² (409,835 sq mi) basin is flat, low-lying and far inland, and receives little direct rainfall. The many rivers it contains tend to be long and slow-flowing, and carry a volume of water that is large only by Australian standards.

The Murray–Darling basin is home to many native animal species. The true numbers may not be known, but a fairly confident estimate has been made of these animals and the current status of their population. Among the aboriginal fauna in the region, the study found that there were:

Historical records show that the previous abundances of fish provided a reliable food source. The bountiful fish became concentrated when the early stages of a flood left shallow water across the floodplain. Today, roughly 24 native freshwater fish and another 15-25 marine and estuarine species are existent in the basin, a very low biodiversity.

Four varieties of carp were used to stock up fish dams. Since then they have made their way into the river systems, where they spread quite quickly. Human introduction, possibly by anglers using small carp illegally as live bait has also increased their distribution. These fish are very mobile, as they can travel easily on flood waters and their eggs can be transported by birds.

Carp are a problem because they feed by sucking gravel from the river bed and taking all the edible material off it, before returning the rest to the water. This stirs up all the sediment, reducing the quality of the water. When caught by fishermen, carp must be killed by law. A project for developing daughterless carp shows promise for eliminating carp from the river system.