The government last month announced it would dredge the channel in the first half of 2022 and remove enough sand to fill 20 Olympic-sized swimming pools.

NSW Maritime is conducting a Review of Environmental Factors, which is expected to be complete by next month, before it calls for tenders for the work.

Marine Rescue Lake Macquarie commander Malcolm Druce said this week that fast-moving tides were shifting sands quickly, causing worsening trouble spots for skippers in the channel.

He said two areas had ridges that were only 1.6 metres deep at high tide. And the water running past the rescue service base at Pelican during the change of tide was reaching four knots, which was "really racing".

"When the tide is moving that fast, the sands are readjusting very quickly," Mr Druce told the Newcastle Herald.

"It's silted up very, very quickly. It's a bit hit and miss whether you get through [the channel] or not, to be honest.

"It would be fantastic if we could have got the dredging done before the summer season, but that's not the case so we've just got to roll with it.

"I've got faith [NSW Maritime is] working as fast as they can. From our perspective, it's not ideal to be dragging people through the channel. I suspect we'll be doing a lot more between now and the dredging."

Mr Druce said some skippers had been cancelling their bridge bookings because of the state of the channel - 14 had cancelled in a single week earlier this summer.

"We are seeing some people go 'this is just way too hard' and keep going up the coast, which is a shame," he said. "Facilities around the lake need people to spend their money here."

In a statement last month announcing the funding for dredging, NSW Maritime's acting executive director Darren Wood said the Swansea Channel was a top priority.

"Funding had been allocated for a major dredging campaign of the Swansea Channel in 2022, improving the functionality necessary to maintain navigation channels and provide access to Lake Macquarie that has become restricted by natural sand shoaling," he said.

"The Swansea Channel is [entry to] the largest coastal saltwater lake in the southern hemisphere, and is two times the size of Sydney Harbour, and we understand that maintaining ocean access through the narrow passage is of major importance."

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