Port Macquarie-Hastings Council contractors started the seven hour epic dig at 8am on Friday morning (May 22). By 3pm - the last scoop of sand was lifted from in the scrape of the entrance and water flowed.

The effect was immediate and the dozens of spectators lining the headland and beach to watch rejoiced. Within minutes, bodyboarders were riding the waves.

And while it was not the traditional excavation of a deep channel that has been implemented in lake openings of the past, it was enough.

A council spokesperson said it is likely to be several days before the real impacts of the berm scrape can be assessed but the reduction of flooding around the lake's perimeter is likely to happen swiftly.

Large swells over the weekend may also gouge a wider channel and infiltrate the lagoon with fresh seawater.

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Natural resources manager Blayne West said the action taken by council will have an immediate impact on the lake while being environmentally sympathetic to the ecology that depends on water being in it.

The sand excavated in the scrape may be moved further down the beach for nourishment.

"Every time we make an action we have an environmental impact," Ms West explained.

"We know people like to recreate in this space but we need to balance the recreation of the community with the ecological impacts - this achieves both of those outcomes.

"Our biggest priority here is flood mitigation. If we get back to the 1.6m trigger and properties are flooding council will come back and do this again. We will do it as many times as we have to."

Council has a 12 month short term licence from Crown Lands to conduct emergency lake openings for flood mitigation only. The trigger point for an emergency opening is 1.6m.

Residents Margaret Cook and Cynthia Hanington have watched the lake's disposition change and evolve over the years. Both holidayed at Lake Cathie as children and have lived in the region all their life.

"We would come here when we were kids," Cynthia said.

"I don't think this will improve it much. The lake doesn't look like itself - it's the opposite of what it should be."

Margaret said the lake to her memory always flowed out to the sea and stayed open for long periods of time.

"We always had to be careful swimming because of the flow and there is a deep hole in the middle," she said.

Both hoped the lake will rejuvenate in time for the holidays, adding Lake Cathie is a beautiful place for families to gather with their children.

Cr Peter Alley was at the beach all day speaking with residents about the decision made by council.

"The vibe here is generally positive," Cr Alley said.

"People are excited - someone even described it as being like a barn-raising.

"There is a lot of opinion about how we could or should have done it but 400mls is going to come off the top of the lake over the coming days."

Revive Lake Cathie spokesperson Kay Aston said the action on the lake, while a long time coming, is a positive sign people are listening.

"This is about the environment and the best we can do for Lake Cathie, the Lake Innes estuary system and we are doing it together."

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