Potentially toxic algae has been found in the Darling-Baaka River in outback NSW, as small clusters of dead fish wash up a fortnight after a historic mass kill.
Millions of dead fish surfaced at Menindee weeks ago due to low levels of dissolved oxygen in the water, known as hypoxic blackwater, a condition made worse by prolonged floods and unseasonal heatwaves.
Premier Chris Minns and NSW Environment Minister Penny Sharpe visited the town in the state's far west on Wednesday to meet locals and announce the government would commission a review into the fish kills, the worst on record in the region.
The state's Environmental Protection Agency on Thursday told the community six samples taken from the river on March 21 contained potentially toxic algae and blue-green algae.
Large blooms of blue-green algae were partly blamed for a mass fish kill at Menindee during severe drought in the 2018-19 summer, when the river was low or had stopped flowing.
The agency said results of metal and nutrient testing were not yet available, but preliminary results were negative for pesticides.
The Department of Planning and Environment said small clusters of dead fish, in their tens or hundreds, washed up near the town on Tuesday.
Water sampling showed dissolved oxygen dropped to critical levels in some areas, so flows of oxygenated water from Lake Pamamaroo were increased.
"We are aware that we need to balance water releases to improve water quality for fish and aquatic health, while also maximising storage ahead of any future drought sequence," the department said in a statement.
Authorities and river experts met with community members on Thursday morning to share the results
Residents have been concerned about the safety of their drinking water for weeks, and the local council has been carting treated water to households who rely on the river.
Essential Water and NSW Health said the water from the town's treatment plant was safe to drink and monitoring was increased to ensure it met Australian drinking water guidelines.
An emergency operations centre will stand down this week, as NSW Police say their priorities to remove as many fish as possible and protect drinking water have been fulfilled.
Assistant Commissioner Brett Greentree said 10 tonnes of dead fish were taken to landfill, while state and federal authorities continue to monitor water conditions and river health around Menindee and further downstream
"I want to reiterate that while the emergency operation is concluding, there will still be significant work being conducted by the responsible agencies throughout the Murray-Darling Basin and beyond," Mr Greentree said.
