Bushfire runoff impacting water quality in Hume Dam and downstream

The Murray-Darling Basin Authority has been working to relieve the impacts of last summer’s bushfires on water quality downstream of Hume Dam.

Monitoring has found oxygen-depleted water as well as 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.

MDBA Executive Director of River Management, Andrew Reynolds, said there is little that can be done to improve water quality in the dam, but the MDBA has been modifying water releases to help boost oxygen levels as water leaves the dam.

“This week we’ve been releasing water from the valves which injects more air into the water, raising oxygen levels as water leaves the dam – and we have already seen it working, with oxygen levels returning to more normal levels downstream. This is also helping water supplies into Albury,” Mr Reynolds said.

Mr Reynolds said the MDBA is working with the states to increase monitoring and testing both in the lake and downstream of the dam.

“We’ve increased testing and found there is good quality water at the top of the dam with high oxygen levels, but below 20 metres, we discovered poor oxygen levels and minerals like iron and manganese,” Mr Reynolds said. “This increased testing regime will continue for some time now as we monitor this situation closely.”

“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.

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

“Unfortunately, as this is a natural phenomenon across a large body of water there are limited options for preventing it,” Mr Reynolds said.

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,” Andrew 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. At this point in time Wodonga’s treated water is not impacted.

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