On Friday morning, work began to remove the sand plug that has been stopping the ocean water from flowing in.

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On Friday, a small channel was open, and Fraser Property's Shell Cove Development Director Simone Dyer said they won't be rushing to dig out the sand.

"It will probably take a few weeks to do the rest of the channel entrance excavation and the excavation of the plug," Ms Dyer said.

"We've just had approval to start the tidal exchange and we'll be controlling this notch over the coming weeks until the plug is completely removed.

"It's a very controlled environment to make sure there's no turbidity or disruption of the natural marine environment so that the exchange occurs in a very orderly and controlled manner."

Ms Dyer said the sand plug had been in place while the harbour facilities were built in a dry environment.

Since completion of that work, the harbour itself has been allowed to fill up with treated stormwater - it is the outlet for a 3.5 square kilometre stormwater catchment.

"Once we open the sand plug there will be a tidal exchange of ocean water and clean stormwater and that will create the tidal estuary in perpetuity," Ms Dyer said.

Once the harbour is filled, the water level will rise and fall with the tide but the average depth will be four metres.

The opening of the harbour to the ocean is a major stage in what has been a long-running project.

So long in fact that current Shellharbour Mayor Marianne Saliba's mother May Hudson discussed the issue when she herself was a councillor back in the 1990s.

"I'm really proud to be at this stage," Cr Saliba said.

"I know that there have been cynics who said it was never going to happen, we're never going to have the harbour. I guess there were times when it seemed like that.

"There was a process that we had to go through, a process not only for the development of the town centre but also a process of raising the funds to be able to do the work here in the harbour."

As well as the facilities to dock vessels in the marina, Cr Saliba said there would also be dry storage where small boats could be lifted out of the water and stored in a purpose-built facility.

Cr Saliba said it could be just a matter of months before boats are sailing in and out of the marina.

"I'm hopeful it will be before the end of this year, maybe around October.

"We've got a lot of people who own boats who have been asking about this - 'when's it going to happen?'.

"We will soon be able to offer people berths to put their boats in."

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