The NSW Environment Protection Authority (EPA) has brought a case against an electricity company over a mass fish kill in Lake Macquarie.
The deaths of thousands of fish on the shores of Lake Macquarie in August 2022 was initially found by the EPA to have been a "natural event".
Now, a filing by the EPA in the NSW Land and Environment Court alleges Delta Electricity, the company operating a power station at nearby Vales Point, was to blame for the environmental damage.
The September 5 court filing alleges chemical leaks originated from Vales Point Power Station, a coal-fired power station at the southern end of Lake Macquarie.
The EPA accuses Delta of failing to properly maintain a chlorine dosing plant at the power station, which resulted in the discharge of "concentrated sodium hypochlorite" – a compound used in chlorine – in waterways connected to Wyee Bay.
The EPA believes this leak was the cause of the wildlife deaths, including thousands of fish and stingrays.
"Our investigation found that Delta could have prevented the fish kill if they had adequate equipment and processes in place," NSW EPA chief executive Tony Chappel said.
The EPA alleges the incident was a breach of Delta's environmental protection licence and if the court rules in its favour, Delta Electricity could be hit with fines of up to $1 million.
Delta Electricity said it was aware of the case against it.
"Delta takes these allegations seriously and is currently reviewing the details of prosecution which have now been provided by the EPA," it said in a statement.
"As the matter is now before the courts, it is inappropriate for Delta to comment further at this time."
Chlorine dosing plants are seen as a standard system across coal-fired power plants.
Chlorine is used to treat the water intake into the coal station's boilers and remove impurities from the lake water.
Vales Point has been in operation since 1998 and provides 1320 megawatts of capacity to Australia's national power grid.
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The EPA said water quality in Lake Macquarie had since returned to normal levels after Delta Electricity upgraded its systems.
The EPA chief executive thanked the community for its patience throughout the investigation, in what he described as a "distressing event for the community".
The case will now proceed through the NSW Land and Environment Court.