The Environment Protection Authority claims that the outcome of fish autopsy analysis has reinforced its previous findings that the mass fish kill in Lake Macquarie at Mannering Park was a natural event.
EPA officers, Central Coast Council and NSW Fisheries collected fish and water samples for laboratory analysis when hundreds of dead fish and other marine life was found along the shores of Wyee Bay early in August.
Results of extensive water sampling reported last week in the Coast News showed there were no significant finding of pesticides, metal or toxicity, however, Total nitrogen and Total phosphorus levels were above guidelines which the EPA said might indicate disruption of sediment.
Earlier this week the EPA released test results of fish and marine life collected from locations at Kevin St, Vales Point, Wyee Bay Marine and the Vales Point Power Station hot water discharge point.
The dead fish and an eagle ray were tested for the presence of pesticides, metals and inorganics through examination of their gastrointestinal tract, gills and liver.
“Results of the water and fish samples, along with the analysis of weather conditions at the time, indicate the most likely cause of the deaths was from a combination of factors,” an EPA spokesperson said.
“The bay at Mannering Park has elevated temperatures compared to the rest of Lake Macquarie due to the water discharges from Vales Point power station.
“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, acclimatised to higher temperatures.
“We know the important role Lake Macquarie and the bay plays in the community and the region’s wider environment and have deployed a ‘smart buoy’ at Wyee Point to allow ongoing monitoring in the coastal lake.”
The EPA spokesperson says it has worked closely with the Department of Planning and Environment – Science, Biosecurity, Food and Fisheries and Central Coast Council on the investigation that produced these findings.
Detailed results of the water and fish testing is available on the EPA website.
Sue Murray