Lake Macquarie fish kills

20th October 2022

Mr GREG PIPER (Lake Macquarie) (18:02): I have never been too shy in regaling the House about the beauty of Lake Macquarie and all the reasons so many people want to live along the beautiful waterway. But we have had two concerning incidents recently which serve to remind us that it is a fragile natural system that needs careful management and constant attention. Those two incidents involved the undetermined deaths of many thousands of fish in an area known as Mannering Bay at the southern end of the lake. The Environment Protection Authority, or EPA, is still investigating the possible causes of those events, and I will return to that investigation shortly.

It goes without question that Lake Macquarie residents are understandably concerned about those incidents and want answers. In the vicinity of Mannering Bay is the warm water outlet from the neighbouring Vales Point Power Station. I make that point as the warm water attracts many exotic species of fish which are normally found in the tropics and not in this part of the world. In fact, some lucky locals will say that some of their best days on the lake are the days they see a rare spotted eagle ray leaping from the water around Mannering Bay and gliding through the air before diving back into the water. Seeing those types of creatures among the dead fish washed up on the shoreline in recent months has been a shock and distressing for many.

The first fish kill occurred in early August when thousands of dead fish floated to the surface and onto the shores. The EPA began investigating the same day and reported several weeks later that the likely cause was a natural event. Shortly after that, in early September, a similar event occurred in the same spot. The EPA's investigation into the second incident is not yet finalised but it appears that it has been more thorough than the first investigation, which is understandable. In its initial findings into the first event, the EPA found that while there was no clear cause, the kill was likely the result of a combination of factors combined with weather conditions at the time.

Given the flooding that occurred several weeks prior, the EPA believes the kill was likely due to a rapid turnover in the water column combined with high ammonium concentrations and the disturbance of sediments, which could have released sulphides that overwhelmed the fish. As I mentioned, we are still waiting on the results of the second investigation by the EPA, Central Coast Council and the Department of Planning and Environment's science, biosecurity, food and fisheries experts. We know already, however, that the investigation has included the inspection of property, machinery and data records of the nearby power station. I hasten to add that the power station has been a cooperative participant in the investigation and there is currently no evidence that the plant has contributed in any way to the fish deaths. The EPA has also installed a custom-built buoy in Mannering Bay, which is now providing real-time data on things such as salinity levels, turbidity, oxygen levels, temperature and pH levels in that part of the lake. It is fantastic technology.

While we keenly await any new findings, we are reminded of what a fragile system Lake Macquarie is. Particularly when first elected, I reported to the House many times about the health of the lake. I was involved for many years in the fight to save this important waterway from the degradation visited upon it since white settlement. Industries such as smelting, power generation and coalmining, combined with the run-off from unsealed roads and road verges and the lack of sediment controls on building sites—which were booming in the 1960s, seventies and eighties—all had a huge impact. Of course, the nutrient inputs of phosphates and nitrates coming from onsite effluent disposal and people greening their lawns absolutely drove increases in large algal blooms. It really was a mess.

The council and the State did eventually jointly carry out restoration works. The outcome was the rehabilitation of 15 State significant wetlands and 38 kilometres of foreshore, the installation of more than 70 stormwater treatment devices and the planting of 600,000 endemic plants, among many other things. The lake became a benchmark for other restoration projects not just in New South Wales but also around the world. Indeed, it was internationally recognised for its excellence. The health of the lake was turned around. Anyone will tell you that today it is one of the best estuary systems you could wish to find in Australia and the world. With more than 200,000 people now living in the catchment of the lake—and many more visiting from far and wide to enjoy the waterway—we need to keep a focus on protecting this fragile ecosystem to ensure that fish kills such as we saw recently do not become a common experience in the lake.

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