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Rain causes water quality challenges in Murray-Darling Basin

Widespread rain during the past fortnight has been a catalyst for more fish deaths in New South Wales (NSW), according to the Murray-Darling Basin Authority (MDBA). 

MDBA Executive Director of River Operations Andrew Reynolds said it was a “cruel twist but an unavoidable risk” that the much-needed rain had contributed to fish deaths in areas where ash and sediment were washed into waterways.

"We have seen fish deaths in recent weeks in several locations under stress due to fires and the ongoing drought – in the Macquarie River, the Namoi, Gwydir, Border Rivers, Barwon–Darling, Lachlan, Upper Murray and Murrumbidgee rivers, and the Lower Darling continues to be an area of concern," he said.

"Basin governments are on the ground working hard to relocate fish, install aerators and deliver strategic releases of water for the environment. Working with relevant state agencies, the MDBA is continuing to monitor the impacts on the Basin's water quality and quantity.”

Earlier this month, the New South Wales (NSW) Government announced it had put measures in place to protect Sydney’s drinking water supply from ash and debris from the bushfires.

This included placing silt curtains and booms at Warragamba Dam to help stop the flow of ash into the system. Water NSW scientists were also monitoring water quality in key supply storages in real-time. 

Minister for Water Melinda Pavey said the government’s priority was to protect Sydney’s drinking water.

“We have worked closely with the Rural Fire Service to ensure fire retardant chemicals used near Warragamba Dam are appropriate, and that exclusion zones were in place to avoid the use of retardants in close proximity to water where possible,” Pavey said.

“The NSW Government is also assisting local councils as the utility providers in areas affected by the recent fires by deploying resources to help with the management of their water supplies, including carting water where necessary.”

Other risks

While offering welcome relief from the bushfire crisis and severe drought, the MDBA’s Reynolds said the rain had so far had little impact on overall storage levels in the Basin, which are at a combined 27% capacity.

“Though some catchments will see levels recover slightly over coming weeks, the total volume of water in Basin storages continued to decline over the past fortnight,” he said.

"We really need a long period of above-average rainfall to break current drought conditions."

He said areas in the Basin with reduced and no flows were also at risk of algal blooms

There are a number of sites in NSW with a blue-green algae alert, including: Menindee Lakes at Lake Wetherell, Darling River at Louth, Burrendong Dam and Namoi River downstream of Lake Keepit.

Victorian sites with a blue-green algae red alert are: Tullaroop Reservoir, Lake Eppalock and Gum lagoon in the Torrumbarry Irrigation Area.