Bushfire runoff is impacting water quality in the Hume Dam and downstream areas of the Murray-Darling system. 

Monitoring has found oxygen-depleted water and increased levels of iron and manganese in a deeper layer of Hume Dam – the source of water for Albury and Wodonga and downstream communities and irrigators.

The Murray–Darling Basin Authority (MDBA) has been modifying water releases to help boost oxygen levels as water leaves the dam. However, the authorities say here is little that can be done to improve water quality in the dam.

The MDBA is working with state governments to increase monitoring and testing both in the lake and downstream of the dam.

“Our concern is that as we enter autumn and the water in the Hume Dam cools, it may begin to turn over, mixing that oxygen-depleted layer with the oxygenated water above, and reducing the water quality throughout the lake,” says MDBA Executive Director of River Management, Andrew Reynolds.

“If this occurs and the oxygen in the water reaches a certain low level, we could see fish deaths occur.”

It is believed the cause of the issue is runoff from the bushfire-impacted areas of the catchments upstream of the Dam. In the 2019-20 fires, 57 per cent or 500,000 hectares of the Upper Murray - the area surrounding the rivers that supply water to the Dam - was burnt.

“Rain carrying bushfire debris into waterways can cause a chemical reaction that leads to low dissolved oxygen levels and high levels of minerals in the water such as manganese,” Mr Reynolds said.

Albury City Council is responsible for supplying water to the city and has notified customers that despite discolouration the city's treated water remains safe to drink. Elevated manganese and iron are unlikely to pose a risk to health. The authorities say Wodonga's treated water has not been impacted.