Despite heavy rainfall earlier in December, it failed to bring water levels in the lake to the emergency flood mitigation trigger of 1.6 metres AHD (Australian Height Datum) - the level at which council has resolved to open the lake to protect critical infrastructure and community assets.

"Over recent days, lake levels have fluctuated from a high of 1.3 metres around mid-December to 1.28 metres as of December 21," a council spokesperson said.

"These higher water levels and the recent fine weather have generated improved conditions for recreation, such as bird watching, kayaking and paddle boarding.

"The BOM's prediction is for above average rainfall over the next three months from January to March so close monitoring of the water levels will be undertaken to address any potential flood impacts."

Local government legislation allows for council to access the beach to mitigate against flooding when water levels reach 1.6 metres AHD.

An attempt was made prior to Christmas by unknown residents to dig a shallow channel from the lake to the shoreline. It was unsuccessful.

Community advocacy group Revive Lake Cathie (RLC) this month recorded an ammonia spike in its December NSW Waterwatch testing results.

RLC's marine biologist Dr Deb Geronimi qualified December's water samples.

"These results continue to evidence the overall lake's health as very poor and an unexpected spike in ammonia levels, higher in some areas than last month, despite recent rainfall," she said.

"December's results show that possible seepage from sewerage contamination could be occurring in the lake system. These results have now been supported by community reports of sewerage smells in this Lakeside Way area."

RLC has called on council to open Lake Cathie lagoon and/or put-up warning signs to advise the community that swimming and consuming fish from the lake could be detrimental to their health.

Ahead of any future flooding scenario, council said it is hopeful of being able to proactively undertake a planned 'dry scrape' of the sand berm separating the lake and the ocean prior to the 1.6 metre AHD level being reached.

"This practice of dry scraping, where a wide section of the berm is excavated to 1.6 metres AHD, is based on the best current advice from the Department of Primary Industries and Fisheries (DPI)," the spokesperson said.

"It is consistent with approaches taken at other Intermittently Closed and Open Lakes and Lagoons (ICOLLs) in NSW. Council has applied to the NSW Department of Planning for a Crown Lands licence to undertake these works."

If successful, the licence will allow council to pre-emptively scrape the sand berm by more than half of one metre to 1.6 metres AHD - allowing the lake to mimic a natural process where it will naturally overtop the berm when water levels and conditions are right.

This approach is preferred by DPI Fisheries, the National Parks and Wildlife Service and the Department of Planning, Infrastructure and Environment given the sensitivity of the Lake Cathie and Lake Innes system to rapid water level changes.

"We believe this approach gives the system and Lake Innes Nature Reserve the best chance to recover from the acid sulphate and iron floc issues that were experienced following the 2019 drought and subsequent openings," the council spokesperson said.

"Undertaking any works without a Crown Licence is an offence for which penalties apply. This includes any illegal opening attempts made by the community which may also result in serious safety risks as well as negative environmental impacts on the lake.

"Over the coming weeks, council will continue to monitor for changes in lake levels resulting from sudden or prolonged rainfall events, note Bureau of Meteorology rainfall forecasts and we will update the community in regards to any necessary action."

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: