The Macquarie-Castlereagh catchment is situated in central western NSW and is based around the Castlereagh, Macquarie and Bogan River valleys. The catchment rises near Oberon on the western side of the Great Dividing Range and flowing to the Barwon River near Carinda. The catchment is flanked by the Barwon-Darling catchment to the north and west, the Lachlan to the south and the Namoi to the north.
The Macquarie-Castlereagh catchment covers 91,985km2 (or 8.8 per cent of the MDB area) and contains two major storages, Windamere Dam (capacity 368 GL) on the Cudgegong River and Burrendong Dam (capacity 1,188 GL) on the Macquarie. There are several distributary rivers and creeks that enter the Macquarie river, including Bell, Little and Talbragar Rivers. The landscape of the Macquarie-Castlereagh region varies markedly from east to west and grades from the headwaters (or tablelands) to plains in the west. The Ramsar-listed Macquarie Marshes are located in the far west of the catchment. Since the construction of the Burrendong Dam in 1967, the Macquarie Marshes have declined significantly in health, as it has caused a significant change to natural water flows in the system and specifically to the Marshes.
A cold water pollution curtain installed in Burrendong dam in May 2014 to reduce the effects of cold water being released downstream on native fish species in the Macquarie River. This is anticipated to improve native fish habitat within the river below the dam, improve the condition and extent of emergent, submerged and riparian vegetation communities and support the habitat requirements of native fish and other native species; including frogs, turtles and invertebrates.
During 2014-15 a key Annual Basin Priority for the Macquarie was to restore a more natural flow regime and address cold water pollution.
Glossy ibis at Buckiinguy Swamp, Macquarie Marshes, 2014
The Macquarie-Castlereagh catchment is an ecologically significant area because it includes:
- wetlands of international significance listed under the Ramsar Convention
- other flow-dependent assets including the Macquarie River channel, the Lower Macquarie River, and the Effluent Creeks (e.g. Marra Creek, Crooked Creek and Duck Creek) on the western side of the Marshes
- a diverse range of vegetation including river red gum forest and woodland, black box woodland and lignum
- migratory bird habitats
The region contains one of the largest and most important wetlands in the Murray-Darling Basin, the Macquarie Marshes. Approximately 200,000 hectares of the Marshes have been listed as nationally important in the Directory of Important Wetlands in Australia (DIWA), while some 18,700 hectares of the Macquarie Marshes has also been listed under the Ramsar convention. The Ramsar listing consists of three separate reserve areas: the Northern Marsh, Southern Marsh and Eastern Marsh.
The Macquarie Marshes contain a wide range of vegetation types, determined by the frequency and duration of flooding. These include river red gum woodland, water couch grasslands, extensive beds of common reed, coolabah, black box, lignum, reed swamp, cumbungi and river cooba.
The range of vegetation found throughout the wetlands provides habitat for many species including 211 bird species (including four waterbird species listed as threatened in NSW), eight species of native mammal, 15 frog species, 56 reptile species and 24 native fish species. Seventeen waterbird species of the Marshes, including the black-tailed godwit and fork-tailed swift, are listed on the JAMBA, CAMBA and/or RoKAMBA international migratory bird agreements.