The Lachlan Valley catchment in central western NSW centres on the Lachlan River. It is bounded to the east by the Great Dividing Range, to the north by the Macquarie, to the south by the Murrumbidgee and the north-west by the Darling catchment. Rising near Gunning in the east, the Lachlan River travels around 1,400 km. The diverse landscape influences the vegetation, which ranges from temperate forests, woodlands and grasslands in the east to semi-arid woodlands, mallee and shrublands in the west.
The catchment area is 86,554km2, or 8.3 per cent of the total MDB area. It is essentially a terminal system with the Lachlan River ending in the extensive wetlands of the Great Cumbung Swamp. The Lachlan River itself is only intermittently connected to the Murrumbidgee River when both rivers are in flood. Tributaries to the Lachlan include Belubula, Boorowa and Crookwell Rivers. The Lachlan catchment is regulated by the two major water storages of Wyangala Dam (capacity 1,220 GL) and Carcoar Dam (capacity around 36 GL), and other regulating weirs such as Booberoi and Lake Brewster.
The Lachlan catchment is an ecologically significant area because it includes:
- wetlands in the lower western region covering 471,011 ha, 95 per cent of which are on the floodplain
- nine areas listed on the Directory of Important Wetlands in Australia (DIWA) with particular value as waterbird and migratory bird habitat
- native fish species including the Australian smelt , freshwater catfish , silver perch , golden perch , big-headed gudgeon and western carp gudgeon
- habitat for threatened species, such as Sloane's froglet, Australian painted snipe, osprey, blue-billed duck and the fishing bat
- areas of river red gum forest and woodland, black box woodland and lignum.
The nine nationally important wetlands in the Lachlan catchment are: Booligal Wetlands, Murrumbidgil Swamp/ Lake Merrimajeel, Cuba Dam, Merrowie Creek (Cuba Dam to Chillichil Swamp), Great Cumbung Swamp, Lachlan Swamp, Lake Brewster, Lower Mirrool Creek Floodplain, and Lake Cowal/Wilbertroy Wetlands. The Booligal Wetlands and the Great Cumbung Swamp are notable sites as both wetlands are well known for providing habitat for both large numbers and species of waterbirds, particularly straw-necked, white and glossy ibis, when the area is flooded. The catchment has been recorded to support 80,000 breeding pairs of ibis. The Great Cumbung Swamp also contains one of the largest stands of river red gums in NSW.