More fish deaths expected as mercury rises

As Australia braces itself for another hot, dry summer, farmers and those in rural communities are being warned to expect another string of fish deaths due to the ongoing effects of the drought.

In December 2018 and January 2019, the lower Darling river system played host to three tragic fish deaths that covered a 40km stretch of the Darling River, downstream of the Menindee lakes.

Following the mass deaths, there was an outcry from farmers and community members who raised concerns over management of water in the region.

The Federal Government appointed an Independent Panel to determine the cause of the fish deaths and what could be done to manage future events. The Panel released its findings in March 2019 which stressed the ongoing effects of the drought as a major factor.

With no rain in sight and a massive heatwave expected to hit the East Coast of Australia this summer, the Murray Darling Basin Authority has urged people to expect more fish deaths this summer.

“We are already seeing the drying of critical aquatic refuges in the north, and water quality issues such as blue-green algae and stratification are becoming more widespread,” the MDBA said.

Although there are a number of causes behind fish deaths, the Independent Panel report found that the fish deaths in the lower Darling rivers were specifically caused by drought conditions.

The Panel explained that there had been no significant inflow into the Menindee Lakes since 2016 which, combined with extended hot and dry weather conditions, resulted in poor water quality issues.

These conditions caused algal blooms (a rapid growth of microscopic algae) to develop over time and by late 2019, water quality in the lower Darling rivers were at ‘red alert’.

In conjunction with these conditions, abrupt reductions in air temperature and increased wind associated with storms, caused the weir pools to destratify (the separation of lakes into three layers), resulting in low oxygen water.

Efforts are already underway to prevent more mass fish deaths in Minindee with local authorities installing pontoon aerators to oxygenate small sections of the river in an attempt to create areas of refuge for fish.

The NSW Department of Primary Industries (DPI) has installed four pontoon aerators and two large-scale pumps in the Menindee region with an extra four placed downstream in the Darling River.

Despite these efforts, without fresh water flows into the river, more fish deaths continue to be a likely risk this summer.



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