In 1902 the New South Wales government built a weir and regulator to channel water from the Lachlan into the Lake Cargelligo for storage, and in 1946 modification of Lake Ballyrogan was started. The work was finished in 1952 and the Lake renamed Brewster after the Department’s chief engineer of the time.

Lakes Cargelligo and Brewster are valued wildlife and recreation areas. Lake Brewster is a wildlife refuge and the birds which enjoy total protection here include the Australian pelican, black swan and great crested grebe. The lake in 1989 was Australia’s major rookery for the pelican, thanks to the five months of high water levels following consistent rain.

The large, shallow Lake Brewster can hold 153,000 mega litres of water. The lake covers 6100 hectares when full and was formed by the construction of embankments to contain flood flows.

Lake Brewster is shallow and not used for boating. The Department of water resources maintains a picnic area by the weir, with barbecue facilities. There is no proper camping ground, although the department permits overnight camping.

The weir and earth dam at a bend on the Lachlan raise the river’s level so that water flows down the channel to the lake. Lake Brewster is principally irrigation storage but it also mitigates flooding by holding water that would otherwise wash down the lower Lachlan Valley.

Lake Cargelligo and Brewster both accept water from the Lachlan when the river is running high and release it when required for irrigation of the lower Lachlan Valley.

Cargelligo’s water complements Brewster’s and, if necessary, further supplies are realised from Wyangala Dam up-river.