The lake has all but closed at the entrance after being manually opened in January 2021 under Port Macquarie-Hastings Council's short term licence for flood mitigation intervention.

The licence was granted by Crown Lands in May 2020.

Crown Lands granted council conditional approval to open the ailing waterway at Lake Cathie last year following a council decision on May 6 that provided the community assurances the lake and its future was a priority.

Council resolved to open the lake if 10mm of rain fell in one weather event or Crown Lands gave them the nod. The current trigger for proceeding with an artificial opening is when the lake level exceeds 1.6 metres AHD.

The berm was scraped on May 22, 2020 forming a deep channel and draining the lake of floodwater. Another scrape was carried out in January this year.

Revive Lake Cathie says its latest request for a lake opening aims to achieve a balance for both the community and the environment.

President Danielle Maltman said it was important to ensure a healthy lake in the lead up to the busy post-COVID Christmas holiday period, while also considering the long-term impacts on marine life when the lake remains closed.

"Opening Lake Cathie lagoon is a short-term remediation action, and we again inform our community that the lake will not improve its current condition until a holistic plan is implemented once Port Macquarie-Hastings Council completes their Coastal Management Plan," Ms Maltman said.

Council director of infrastructure services Melissa Watkins said the lake, as an intermittently closed and open lake and lagoon (ICOLL), will naturally alternate between being open and closed to the ocean because of the sand berm at the entrance and catchment inflows from prolonged rainfall.

"Port Macquarie-Hastings Council undertakes artificial intermittent openings and closing of Lake Cathie to mitigate flood risks, only," Ms Watkins reaffirmed.

"The current trigger for proceeding with an artificial opening is when the lake level exceeds 1.6 metres AHD. At this level, council will undertake works to lower the level of the sand berm to facilitate a natural opening in accordance with the requirements placed on the licence issued by NSW DPIE-Crown Lands, the owner of the waterbody.

"Current advice from Professor Scott Johnston at Southern Cross University is that the lake is still recovering from the impacts of the extreme drought in 2019 on acid sulfate soils. Recent research by Southern Cross University has found shallow groundwater on the edges of the lake channels have very high levels of dissolved iron."

Ms Watkins said residents must understand that any artificial opening of the lake to the ocean often leads to a rapid drop in lake water levels.

"If that were to happen now, it would risk causing some of that iron-rich water to seep into the lake, potentially triggering another mass iron floc event, similar to what happened in 2020," she explained.

"Council is currently working on a long-term holistic plan, known as the Coastal Management Program (CMP), for the Lake Cathie/Lake Innes estuarine system by actively engaging with stakeholders, including the community, universities and State Government to understand the system and the impacts of long term management decisions."

Stage 2 (risks and opportunities) of the Lake Cathie and Bonny Hills CMP is expected to be completed in 2022, Stage 3-4 (evaluate and adopt) in 2023 and Stage 5 (implementation ) from 2025 and beyond.

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