BY DAKOTA TAIT
The Environment Protection Authority says the recent mass fish kill at Mannering Park in Lake Macquarie was likely a natural occurence.
They've found no significant pesticides, metals, or toxicity in the water, though results for nitrogen and phosphorus were above guidelines, meaning sediment might have been disrupted.
EPA Director Regulatory Operations David Gathercole says the results, along with analysis of weather conditions at the time, indicate the most likely cause of the deaths was from a combination of factors.
"The bay at Mannering Park has elevated temperatures compared to the rest of Lake Macquarie due to the cooling water discharges from Vales Point power station," Mr Gathercole said.
"A range of fish, including tropical fish, are attracted to the bay due to these higher temperatures.
"The fish kill was preceded by cool nights in the first week of August and a shift to northerly winds, with the strongest winds on August 4.
"This may have caused cold lake water to enter the bay and resulted in a turnover of the water column.
"If this was rapid enough it would have caused a disturbance of the sediments, which explains the high ammonium concentrations observed on August 5, and potentially the release of sulfides.
"Our results suggest the combination of the temperature and sulfide stress likely overwhelmed fish, acclimatized to higher temperatures."
The EPA's now installed a smart buoy at Wyee Point for ongoing monitoring in the lake.
The dead fish have since been removed by Council.
