The deaths of hundreds of fish in Lake Macquarie are being investigated, with the New South Wales environmental regulator looking for “any potential pollution sources” that could have caused the mass kill.
Paul Winn, the lead researcher at the Hunter Community Environment Centre, said “probably several hundred to up to 1,000 fish” had been killed in Wyee Bay, on the southern end of Lake Macquarie near Newcastle, and washed ashore.
The fish killed included bream, mullet, luderick and a whitespotted eagle ray.
The Environmental Protection Agency said it was notified of the fish kill on Friday afternoon. EPA officers have collected fish and water samples for analysis.
“Field officers also noted greying around the gills, which could suggest oxygen depletion,” the agency said in a statement.
A decrease in oxygen content has resulted in many other fish kills, including earlier this year following flooding in northern NSW. Deoxygenation of water is a natural phenomenon that often occurs after heavy rain events.
The fish kill in Lake Macquarie, Australia’s largest coastal saltwater lake, likely occurred last Tuesday night, Winn said.
“One of the concerns we have is that whatever caused the fish kill may not have been in Wyee Bay when the EPA arrived [a few days later],” he said.
Similar fish deaths have previously occurred in Lake Macquarie.
“Wyee Bay, for example, experienced a fish kill back in about 2015, [but] not quite as severe as this,” Winn said.
Jason Nunn of Fishermans Warehouse, on the eastern shore of Lake Macquarie, called on authorities to determine whether the cause of the kill was ongoing.
“It is alarming when we’ve lost that amount of fish,” he said. “It will take years to replace what we’ve lost.”
Nunn also questioned whether other marine animals such as crabs, prawns, or octopuses had been affected.
The location of the fish kill was close to the Vales Point power station, which draws water for cooling and discharges it back into the lake.
“You’ll always see steam rising off the water as the [heated] water enters the lake,” Nunn said.
The Hunter Community Environment Centre measured the water temperature in Wyee Bay on Saturday to be 23C to 24C, compared to a sea temperature of 17C, Winn said.
At high temperatures, there is less available dissolved oxygen in water.
“It also has an effect on cyanobacteria growth … which has a potential to bloom and cause toxicity. It does also encourage further algae growth that can reduce the oxygen in the water,” Winn said, adding that the exact cause of the fish deaths was yet to be determined.
The operator of the Vales Point power station, Delta Electricity, said it was aware of the fish kill event.
Delta’s company secretary, Steve Gurney, said: “There have been no changes to our operations in the last week – we have done our own internal review investigations to confirm that. We have also been in touch with the EPA to provide them with any assistance that they need for their investigation.
“Under our environmental protection licence, we have limits around what the discharge temperatures of our outlet are, and we we stay within those limits.”
The investigation is ongoing.
The EPA said it had “been out in the field again over the weekend collecting further water and fish samples, and seeking to identify any potential pollution sources”.
