Water sampling has been conducted by Revive Lake Cathie and Waterwatch since September with a fish kill reported to the Department of Primary Industries - Fisheries on October 12.

Dr Deb Geronimi said testing results indicate the overall the lake's heath is extremely poor.

"It is an ecological disaster that could have been prevented by opening the lake before the drought," Dr Geronimi said.

"The drought in 2019 caused the water levels to drop, it became hypersaline and the sediments were exposed to the air.

"This exposure to the air activated the acid sulfate sediments. Once it rained these acid sulfate sediments released sulfuric acid into the water, dropping the pH.

"The iron also precipitated out of the sediments as the sulfates were released.

"The rain events diluted the sea water causing it to become freshwater which shocked all of the marine organisms when the lake was closed and a massive die off of aquatic life occurred.

"This constant opening and closing of the lake is not good for the ecology and the organisms that live within and surrounding the lake system".

Dr Geronimi said marine life currently trapped in the closed lake system may not survive under the current conditions.

Replacing the Kenwood Drive bridge over the lake has now become a priority for Port Macquarie-Hastings Council.

Any planned works on the bridge to improve the health of the lake and estuarine environment must align with long-term coastal management strategies in order to be eligible for state government funding assistance for the project.

Testing of a hydro-dynamic model, completed in 2011, will determine the impacts of any potential changes to the lake system as a result of works on the bridge. Those impacts will also determine the most appropriate bridge design and the options available to council before it proceeds with any work.

Those results will feed into council's Coastal Management Plan (CMP) scoping study which is currently underway.

Port Macquarie-Hastings Council has confirmed the timeline for the scoping study is February 2021 and the completion of the hydrodynamic model is likely to be three to four years away if the full suite of background data capture is undertaken.

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