A meeting led by community advocacy group Revive Lake Cathie declared the condition of the lake an urgent public health issue.

The Lake Cathie/Lake Innes stakeholder meeting was held on November 27, bringing together the community, local and state government representatives.

They included Member for Port Macquarie Leslie Williams MP, Port Macquarie-Hastings mayor Peta Pinson, Port Macquarie-Hastings councillors Lisa Intermann and Peter Alley, NSW state departments, Lake Cathie Progress Association, Lake Cathie Fishing Club and Ozfish Unlimited.

Southern Cross University Professor of Geoscience Dr Scott Johnson and Dr Damien Maher explained the impacts of iron floc on the lake and the short term remediation risks on the estuarine system.

May 2020: It's open: lake floodwater at Lake Cathie released to the sea

"Understanding the complexity of the Lake Cathie/Lake Innes estuarine system is crucial as risks can be multiple and cascading," Dr Johnson said.

Revive Lake Cathie president Danielle Maltman said the NSW Department of Public Health must also step into the discussion.

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.

"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.

Read more: Scraping the lake "experimental" but it's supported by logic

The lake was artificially opened to the sea in May 2020.

Council has a 12 month short term licence from Crown Lands to conduct emergency lake openings for flood mitigation only. The trigger point for an emergency opening is 1.6m.

Council has always maintained that any lake opening must be considered against several risk factors. These include weather conditions and tides, low lake water levels which limit the success of an excavated channel remaining open, the likelihood of excessive sand build up in the recently dredged area and potential risk for red weed to enter and become stuck in the lake should it naturally close quickly.

Council has a management responsibility of the lake in terms of flood mitigation particularly in respect of private property and major infrastructure, and an opening will only occur as an emergency response to the likelihood of flooding of vital infrastructure, such as sewer which is essentially the first level of flood impact trigger before flood levels impact private properties.

Replacing the Kenwood Drive bridge over the lake is also a priority for 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.

The Coastal Management Program (CMP) will set the long-term strategy for the coordinated management of the coastal zone. It will achieve the purpose and objectives of the Coastal Management Act.

It aims to provide a framework for management of the coastal zone, which acknowledges and reflects the needs of the coastal area but balances this with the reality of the competing needs of the region.

The program will identify priority solutions to coastal management in Port Macquarie-Hastings, including the broader issues of the Lake Cathie estuarine system.

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.

Ms Maltman said the three year vision of investigating, planning, implementing and delivery of a long-term sustainability plan for Lake Cathie and Lake Innes is difficult to accept, but the only choice in delivery of an holistic approach.

Revive Lake Cathie is now calling for the Department of Public Health to step in as a key stakeholder and address public health and safety concerns in relation to marine life consumption and water quality risks.

It wants all stakeholders to agree to a long-term sustainable approach due to the acid sulfate soil contamination impacting the entire estuarine system.

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