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Why do we now get fish kills with floods?

Local environmentalists are increasingly concerned at the increase in fish kills over the past 12 years.

Videos and photos have again emerged showing devastating losses of native fish, including Murray cod. They have especially been a problem around Murrabit and Goodnight on the Murray River, and near Kyalite.

Community groups have been using aerators in an attempt to minimise the damage being caused by more regular hypoxic black water events, which reduce the amount of oxygen in the water and lead to fish deaths.

The Speak Up Campaign was approached and asked to highlight the problem, because there were fears the true cause of the fish kills was being ignored.

“We have nine major floods on record from 1931 until 2010 and no record of fish kills,” a concerned resident Matt Heslop said.

“Barmah was declared a National Park in 2010, and from this time grazing and logging was stopped and environmental flows started. From 2010 to 2022 we have had three major floods and three major fish kills downstream from Barmah to Mildura.”

Mr Heslop said in the Murrabit region, Murray cod of 105cm to 110cm have been found dead, as well as many smaller fish of various species. Murray crays left the water, which some believe is an indication that they knew the lack of oxygen was imminent.

“Born and bred locals in the region have seen and experienced many high rivers and floods, but cannot remember black water being present for so much, if any, of our major flood events. It seems that something has changed in water and forest management in the past decade, and it is obviously not doing our river system and fish ecology any favours.

“Surely it is time this environmental experiment is stopped, before we lose more native fish,” another resident said.

In the aftermath of the 2016 flood, hypoxic blackwater killed thousands of native fish, plus birds and other animals.

At the time, the Speak Up Campaign was advised that an Edward Wakool Stakeholder Committee had been preparing a Strategic Adaptive Management approach to the system which could have helped reduce these deaths. However, the committee was disbanded when the Commonwealth Environmental Water Holder withdrew funding and the project’s facilitator, the NSW Government’s Local Land Services Murray, subsequently decided not to continue with the project.

This was despite a report on the project stating that “managing complex systems characterised by uncertainty requires an adaptive, learning-by-doing approach such as Strategic Adaptive Management”, and identified that “management planning for such (hypoxic blackwater) events needs to be prioritised”.

“If the work undertaken by the Edward-Wakool Stakeholder Committee had been allowed to continue, and the action plan finalised and implemented, precious native fish could have been saved,” the Speak Up Campaign said at the time.

“Our faith in the bureaucratic system to effectively manage our rivers correctly has been seriously eroded,” it said.

For several years it has been calling for unintended negative consequences of the Basin Plan to be acknowledged so remedial action can be taken, but says unfortunately it is almost impossible to get those involved in water management to admit mistakes. Therefore, nothing changes.

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