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The Menindee Lakes is a system of 9 large, but relatively shallow lakes, located in south-west New South Wales on the Darling River, about upstream of the Darling River's junction with the Murray River. The Darling River is fed by nine major tributary river systems flowing from south-east Queensland and north and central NSW. The town of Menindee is close to the lakes and Sunset Strip township is on the northern shore of Lake Menindee. The nearest city is Broken Hill.
There are 4 main lakes in the system:
The lakes rely on replenishment, when water flows over the banks of the Darling (Barka) River. The NSW Government modified the lakes (completed 1968) to improve their storage capacity for farming, recreation, mining and urban water supply and to help manage floods in the Darling River. In the 1960s, governments decided to use some of the lakes as water storages, building a large weir (Main Weir) to divert water into lakes Pamamaroo, Tandure and Bijijie. Levees, block dams and channels were built to regulate the flow of water in the system. There is relatively little information on the flooding regimes of the lakes before they were regulated (dammed) in the 1960s but they were undoubtedly highly productive and important wetland systems where many fish were spawned.
The Menindee Lakes Water Storage Scheme water supply to Broken Hill, the lower Darling and to water users along the Murray River in New South Wales, Victoria and South Australia under the Murray-Darling Basin Agreement. Seven of the lakes have been incorporated in an artificially regulated overflow system providing both for flood mitigation and as storage for domestic use, livestock and irrigation downstream. The lakes are also important for . Recent research (Thoms and Delong 2018) found that the food webs have changed in a way that suggests that the ecological resilience of the system has declined.
The lakes were filled to capacity in 2021 with Lakes Cawndilla and Lake Menindee filling completely in early September meaning that the system was filled to over 98 per cent capacity with water flowing into Lake Speculation for the first time since 2012.
Another report, commissioned by the government opposition leader Mr Bill Shorten MP, concluded the deaths were the result of low water flows and hot temperatures causing blue-green algal blooms. The algae depleted oxygen in the river, depriving the fish of necessary oxygen to live. The report also stated, "The conditions leading to this event are an interaction between a severe (but not unprecedented) drought and, more significantly, excess upstream diversion of water for irrigation. Prior releases of water from Menindee Lakes contributed to lack of local reserves."
The lakes range in size from . The largest are Lakes Menindee, Wetherell, Pamamaroo and Cawndilla. These four, with Tandure, Bijijie and Balaka, are part of the Menindee Lakes Water Storage Scheme, with Cawndilla and Menindee also within the Kinchega National Park. Lakes Nettlegoe, Kangaroo, Stir Tank, New and Malta are unregulated. Lake Tandou is managed as irrigated cropland and is no longer subject to flooding.
The shallow margins of the overflow lakes are studded with dead black box trees while the shores are dominated by bluerod and
on 15 August 2011.
In 1949, work began on building dams, weirs, levees, canals and regulators to catch and retain floodwaters. Major works were completed in 1960 and final completion was in 1968. There were electrical upgrades in 2007. The scheme was built by the New South Wales Water Conservation and Irrigation Commission, to manage river flows, town water supplies and other domestic requirements, irrigated agriculture, industry, and flood mitigation. It has become increasingly important for regulating environmental flows.
Construction of the retaining walls required of rock fill, high and long. The average water depth is and, at 100% capacity, the dam walls hold back of water at an average of above sea level. The surface area of the lakes within the scheme is and the combined catchment area is . The uncontrolled concrete spillway with six vertical lift gates is capable of discharging water at .
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