Menindee Lakes water levels drop to lowest in five years as experts warn of mass fish deaths

The Menindee Lakes are a group of connected lakes in western New South Wales that receive water through the Darling-Baaka River system. They act as an important water store during dry periods. Their condition affects native fish, water quality and flows along the river. When the lakes shrink, the risk of environmental damage rises quickly.

The lakes are especially important because water arriving from the river can replenish them and support fish habitat. The article reports that water in the upper lakes has fallen below 250 gigalitres. Experts warn that poor flows can create conditions linked to summer fish kills, including worsening water quality and algal growth.

The system is now under pressure after low rainfall during the past year. Temporary restrictions limit some irrigation use to preserve water for critical human needs and the environment. Experts want stronger limits on upstream extraction during dry periods, while the government is using fish passage and water-quality planning to reduce risks.

The combined volume of the Menindee Lakes fell below 480 gigalitres earlier this month. It was the first time the total had dropped that low since 2021. This figure shows the whole lake system is under serious pressure after a year of low rainfall and limited inflows.

The upper Menindee Lakes have fallen below 250 gigalitres. That is a formal trigger for temporary state water restrictions across parts of the northern Murray-Darling basin. The restrictions limit access for some irrigators. They are designed to keep water available for critical human needs and the environment.

These figures are more than storage measurements. They mark worsening conditions for fish and water quality. Experts warn that, without improved flows down the Darling-Baaka River, the lakes could face summer fish kills. Recent small inflows from Queensland offer some hope, but more water is needed.

Falling water levels can worsen conditions for fish because there is less water available to dilute pollutants and support healthy movement. Shallow, slow-moving water can heat up more quickly. These changes can encourage algal growth and reduce water quality. If dissolved oxygen falls too far, fish may be unable to breathe.

The article gives a local warning sign: resident Graeme McCrabb described the water developing a “real green algal look”. Experts are concerned that low inflows, a hot summer and poor water quality could combine to create another fish-kill event. Fish passage has been installed to improve native fish movement, but it cannot replace missing water.

The immediate risk depends on future inflows and weather. Prof Jamie Pittock said more water must reach the Baaka-Darling River. McCrabb said the risk could be very high in January or February without inflows, while a milder summer would reduce it.

The catchment has experienced low rainfall throughout the past 12 months. That means less water has entered the rivers and tributaries feeding the Menindee Lakes. With smaller inflows, the lakes fall and have less capacity to support healthy conditions through summer. The article does not quantify how much water extraction has removed.

Upstream water use adds another pressure. Prof Jamie Pittock called for state governments to stop irrigators pumping out the first flush of water after a major rainfall event. An expert panel also recommended limiting upstream overextraction during dry periods. These measures would help more water travel through tributaries and down the Darling-Baaka River.

Temporary restrictions now limit access for some irrigators. They aim to preserve water for critical human needs and the environment. However, the government has not implemented the connectivity panel’s recommendations, according to the article. More rainfall, protected inflows and tighter extraction controls would improve the lakes’ prospects.

Menindee experienced catastrophic fish kills in 2018, 2019 and 2023. Millions of dead fish washed up along stretches of the Darling-Baaka River. These events showed how quickly poor conditions in and around the lakes can become a major environmental crisis. They also caused deep concern among local residents and scientists.

Graeme McCrabb was one of the first Menindee residents to raise the alarm about the 2018-19 disasters. After winning the 2023 state election, Premier Chris Minns and senior ministers visited Menindee and promised an investigation. The government later established an expert panel under the northern basin connectivity program.

The panel recommended limiting upstream overextraction during dry periods. Its goal was to maintain flows into tributaries and reduce the risk of fish kills and large-scale drying. The panel delivered its final report two years ago, but the state government has not implemented its recommendations, according to McCrabb.

The first priority is to keep more water moving toward Menindee. Governments can restrict some upstream irrigation use, especially during dry periods, and prevent pumping from the first flush after major rain. These actions would preserve water for critical human needs, the environment and tributaries feeding the Darling-Baaka River.

The NSW government has already imposed temporary restrictions for some water users. It has also installed a temporary fish passage and created a water-quality working group. The passage can improve native fish movement, while monitoring can help officials respond to changing conditions. Neither measure creates new water, so inflows remain crucial.

The expert panel recommended limiting upstream overextraction, but the state government has not implemented those recommendations. Prof Jamie Pittock said major rainfall is needed. McCrabb said recent Queensland rain produced small inflows, but more would be required. A milder summer would also lower the risk.

Drought reduces rainfall, river inflows and the amount of water available for an ecosystem. Heat then warms the remaining shallow or slow-moving water. Warm conditions can favour algal growth, especially when nutrients are available. These pressures can reinforce one another and make the habitat less suitable for fish.

Algae produce oxygen in daylight, but algae and other organic matter also use oxygen, especially at night and as they decompose. If oxygen consumption exceeds replenishment, dissolved oxygen levels fall. Fish may then become stressed, gather near the surface or die. The article’s reference to a “real green algal look” is a warning sign, although it does not provide oxygen measurements.

This interaction helps explain why hot, dry summers are dangerous at Menindee. Low lake levels and poor inflows leave less water to absorb environmental stress. More river flow, protection from excessive extraction and a milder summer would improve conditions. These points combine established ecological knowledge with the risks described in the article.