The lake was opened by Port Macquarie-Hastings Council in May after it was granted a 12 month short term licence from Crown Lands to conduct emergency lake openings for flood mitigation only.

At that time, the lake had reached its 1.6m trigger point and in making the decision to open the waterway to release floodwater, council made clear there could be adverse consequences.

Three months on and the excavated channel has all but closed with community advocacy group Saving Lake Cathie pushing for swift action on the realignment of Kenwood Drive bridge.

Port Macquarie-Hastings councillors unanimously supported the bridge's replacement at the June council meeting, however council asserts the management of the waterway's health is the responsibility of state authorities.

Group manager Debbie Archer said council's ongoing responsibility for management of the Lake Cathie waterbody is strictly limited to flood mitigation and to protect council infrastructure for the safety of the community.

"Council is also the appropriate regulatory authority to investigate pollution from unnatural sources," she said.

"Any actions outside of this scope, including public health issues and natural processes such as water quality, odour, colour, mosquitoes, fish kills, fish health, ecology, salinity, acid sulfate soils and the like, are the primary responsibility of the NSW Department of Planning, Industry and Environment - Crown Land (DPIE) as owner and manager of Lake Cathie, and National Parks and Wildlife for Lake Innes.

"Council's Coastal Management Program that is currently under development aims to set the strategic direction and clarify agency responsibilities for the future management of the Lake Cathie/Lake Innes estuarine system."

A DPIE spokesperson, however, has said council is in fact the managing authority of the waterway and some of the issues with acid sulfate are historic problems.

"The Department of Planning, Industry and Environment (DPIE) has been providing technical advice to Port Macquarie-Hastings Council on the issue regarding acid sulfate in the waterway at Lake Cathie," the spokesperson said.

"Some of the problems with acid sulfate soils in NSW are as a result of past and current drainage and flood-mitigation practices.

"Council is the managing authority of the waterway at Lake Cathie and DPIE will continue to assist."

Saving Lake Cathie spokesperson Stewart Cooper said all agencies must work together for an appropriate solution.

"There is a visible oily scum from the oxidising bacteria of the iron floc," Mr Cooper explained.

"We need to take advantage of the high tides in order to flush the system out. Obviously the case to replace Kenwood Drive Bridge is more relevant than ever before.

"Our poor lake has finally closed again after three and a half months. With the high volume of sand in the system this was unfortunately never going to be anything but a short term solution to the flooding."

In June, Saving Lake Cathie said it contacted council regarding the brown-orange colour of the soil in the lake system and were advised that this was iron floc, a result of acid sulfate soils that were identified as a major concern back in July 2019.

A project to study these acid sulfate soils was approved in October 2019 but DPIE held the investigation until the Coastal Management Program scoping study was completed by council.

"The scoping study was released to the community for feedback which closed on 26 June 2020. Following the community consultation council has continued to work with DPIE and other government stakeholders to finalise the scoping study," Mr Cooper said.

"We are still waiting. It would appear it has taken longer to engage with the state government and get their feedback than it took to write the scoping study in the first place. Similarly, the acid sulfate soil study remains on hold.

"With the lake now closed, the oily orange scum on the surface of the lake, caused by the iron floc, can no longer be flushed out and will now remain.

"Communication from council and state government stakeholders has been non-existent other than the initial warning to not fish or swim in the lake system."

Water testing to analyse the impact of the iron floc was conducted on July 2 with analysis in the hands of DPIE.

"It would appear all roads lead to DPIE. We continue to wait for someone to communicate with the community," Mr Cooper said.

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