Constant opening and closing of Lake Cathie is harmful, according to recent testing by Revive Lake Cathie

The group has undertaken water sampling in both estuarine systems following Port Macquarie-Hastings Council's scraping of the berm in Lake Cathie on Friday, January 8 this year.

A volunteer team has qualified 233 water samples with testing results reportedly showing environmental degradation underway and a need for urgent action.

Revive Lake Cathie marine biologist Dr Deb Geronimi, who holds a Bachelor of Science First Class Honours Degree in marine and freshwater Biology, and a PhD Estuarine Biology, said the samples evidenced the overall lake's health as extremely poor with extremely poor water quality.

"Constant opening and closing of the lake is not good for the ecology and the organisms that live within and surrounding lake system," Dr Geronimi said.

"Addressing environmental degradation in Lake Innes will restore Lake Innes to its former glory as a NSW fresh water lake of national significance and allow Lake Cathie to function as a salt water estuarine lake.

"Once this is achieved, a permanent dredge could be implemented to replicate something like the Back Creek Estuary at South West Rocks".

Preliminary test results showed extremely low oxygen, high sulfates, slightly diluted tannin and acid being released, according to Revive Lake Cathie.

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Port Macquarie-Hastings Council currently measures conductivity, salinity and water height.

A council spokeswoman said council has a management responsibility in terms of flood mitigation particularly in respect of private property and major infrastructure.

"The water quality of an intermittently closed and open lakes and lagoons will fluctuate, influenced by a range of factors such as being open or closed, high or low water, fresh or salt water influences," she said.

"Each phase supports a slightly different ecosystem and the aesthetic qualities of the lake will not necessarily be favourable to recreational users at all times. Best practice management is to interfere as little as possible and allow natural processes to take place. Council only intervenes where the risk of flooding is likely.

"As of Thursday afternoon the lake water levels reached above 1.6m, and as per the Lake Cathie Opening Strategy, which is currently under review, this is our trigger point in proceeding with protocols to manage potential flooding.

"Part of these protocols, and in line with State government advice and approvals, is to scrape the berm to allow the floodwater to escape. We completed the scraping of the berm on Friday.

"A scraping, rather than an opening, allows nature to then take over and open the lake if there is sufficient water coming into the system to force an opening. In this instance the lake level was still rising from runoff and a full opening eventuated."

"Lake Cathie Opening Strategy is currently under review by council and the Coastal Management Program is also in development. The Coastal Management Program will consider input from all stakeholders including relevant government departments and community to identify actions required to manage not only the lake but the entire coastal area considering environmental and community objectives.

"Best practice management of an ICOLL is to intervene as little as possible and this is the action being taken by the state government departments that have management responsibility for matters within the lake."

The Coastal Management Program will be developed in consultation with all stakeholders including government and community, according to the Port Macquarie-Hastings Council.

Council's coastal management plan (CMP) will play a key role in guiding the future management of the Lake Cathie and Lake Innes estuarine system, after councillors unanimously agreed to support the motion at a December ordinary council meeting.

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