The Western Catchment is the largest catchment in NSW, covering some 230,000 square kilometres. It is bounded by Queensland, the Broken Hill railway line, South Australia and the Barwon River.

The Western Catchment includes the Barwon-Darling, Culgoa, Paroo, Warrego, Narran, Bokhara and Birrie river catchments and lower part of the Bogan River Catchment. The Western Catchment takes in all of Bourke and Brewarrina Shires, significant portions of Cobar, Walgett and Central Darling Shires, and most of the Unincorporated Area.