The trigger point for an artificial opening, under Port Macquarie-Hastings Council's own guidelines, is 1.6m.

The Lake Cathie Opening Strategy outlines the lake is only to be opened when the lake water level is at, or exceeds, 1.6m or falls below 0.2 metres with high salinity, if optimal conditions allow.

As of 11am on April 30, the water level was sitting at 1.589m with rain expected this weekend. The lake is already brimming with hundreds of mullet that cannot make their way into the ocean for the annual migration north to spawn.

But it's not as simple as just opening it when triggers have been reached it seems, and the council lake opening strategy is a part of a complex review of environmental factors which will continue to guide any future management of the estuary.

Council has reinforced 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.

At the November 2019 council meeting, council voted in favour of obtaining a one-off licence from Crown Lands to open the lake after Mayor Peta Pinson put forward a motion.

However, before that licence is granted, Crown Lands has instructed council to conduct a substantial review of environmental factors (REF). The last time this was done for the waterway at Lake Cathie was 1995.

Read more: Council's lake data more than two decades old

Crown Lands said the council documents - 1994 Estuary Management Plan, 1994 Lake Opening Strategy and 1995 Environmental Review - are now considered to no longer be valid.

Council has been instructed that its REF must look at factors from Aboriginal and cultural heritage to impacts on shore birds, endangered species and koala habitats; biodiversity loss; impacts of acid sulphate; sand accretion; coastal and tidal factors and climate change.

It is the view of state agencies, the Department of Primary Industries and Environment Biodiversity and Conservation Division (DPIE), that the management of the Lake Cathie entrance is for "minimal interference" and any proposal to open the lake in the absence of a strategy, is the least preferred approach due to the uncertainty about the potential unforeseen environmental impacts.

Community advocacy groups have been working hard for more than 12 months for action on the ailing waterway.

Council unanimously agreed on a way forward at its meeting in May 2019 following a submission from Revive Lake Cathie in response to the council's 2019-20 draft operational plan.

Those groups continue to push for action and transparency on the management of the lake.

Saving Lake Cathie spokesperson Stewart Cooper said the current situation at the lake needs addressing urgently.

Mr Cooper has proposed that council open the lake under State Environmental Planning Policy (SEPP) legislation that permits "emergency works, including works required as a result of flooding, storms or erosion".

"If feels like council has changed the rules and are being deliberately vague. Under the Lake Cathie Opening Strategy when we hit 1.6m its asks if DPI-Fisheries have been advised, if OEH has been advised and if the publis has been notified. Then it can open the entrance and the next suitable run out tide," Mr Cooper said.

"Now, council needs weather and tidal conditions to be right, but don't specify what they are.

"Given the lack of action on dredging will council consider grading the ocean berm rather than digging a channel? This would reduce the risk of emptying the lake due to the high level of siltation.

"We want a reduction in water volume and to let saltwater into the system and allow some of the mullet to get out.

"The last thing we want is to dig a big channel and all the water runs out and we end up with a lake that has no water in it again."

Mr Cooper believes "minimal intervention" at the lake is a furphy when there has historically been significant human impact on the health of the changing waterway. This includes the opening Lake Innes to Cathie Creek reducing tidal flow and converting Lake Innes from the largest fresh water lake nationally to salt water; the construction of Kenwood Drive Bridge which has effectively dammed the lake from the rest of the system; and housing development approval.

The lake briefly opened to the ocean on January 14 as a result of a significant high tide and large swell.

Heavy rain at the end of March this year, has also caused low-lying inundation in some areas and shifted the salinity of the lake to zero.

Council staff are currently developing a Coastal Management Program (CMP) Scoping Study and are currently seeking estimate costs for the undertaking of a REF, according to council's website.

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