Double-edged sword of warm wet summer: working to reduce impacts of low-oxygen blackwater

Department of Agriculture and Water Resources

Commonwealth Environmental Water Office


With high river flows and more rain to come, native fish, crays and river animals all the way up the food chain are enjoying a feeding bonanza. Leaves, grass and other organic matter are being flushed off the floodplains into our waterways, providing food for bacteria, which in turn are eaten by other animals, benefiting the whole river ecosystem.

However, warm temperatures can see the high loads of organic matter decompose too fast and deplete the oxygen in the water – oxygen that native fish and other animals need to survive.

Blackwater – as water rich in organic matter is often called – can become hypoxic (low in oxygen) very quickly in warmer weather and has already led to fish deaths in the Murrumbidgee region this summer.

With the large volumes of water moving across the floodplain at the moment, there is often very little that can be done to prevent hypoxic blackwater developing.

However, DPI Fisheries, water managers, scientists and environmental water holders are monitoring rivers and creeks, and working together to reduce the impacts of hypoxic blackwater where they can. This includes delivering environmental flows to improve dissolved oxygen levels in the Lowbidgee, Yanco and Billabong Creek system, and Bundidgerry Creek.

For example, irrigation corporations have assisted by using their networks of channels and escapes to convey water for the environment to affected areas such as Yanco Creek. By using their networks of channels and escapes, small volumes of oxygenated water have been delivered quickly to where it’s been needed, creating areas of better quality water for native fish and animals to take refuge until conditions improve.

Water for the environment is also being delivered to the lower end of the Murrumbidgee River, downstream of Maude, to minimise the risk of hypoxic conditions developing and dilute the organic-rich water as it returns to the river from the floodplains.

While agencies are on the lookout for poor water quality, locals are also encouraged to keep an eye out. Some of the tell-tale signs that water may be becoming low in oxygen and turning hypoxic include crayfish and yabbies climbing up out of the water and onto banks, or fish gasping for breath at the surface or dying. Anyone seeing these signs are urged to contact the Fishers Watch Phoneline on 1800 043 536.

To find out more about water for the environment, keep an eye out for updates on the Commonwealth Environmental Water Holder’s Facebook and Twitter pages or visit Commonwealth Environmental Water Office.

Blackwater from Cowabbie Creek entering the muddy water of Bundidgerry Creek

Blackwater from Cowabbie Creek entering the muddy water of Bundidgerry Creek. Photo credit: DPI Fisheries.

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