The 55-year-old coalminer from Merewether had just completed an epic 36km swim from Catherine Hill Bay to raise funds for mental health charity Beyond Blue after his dream of swimming the English Channel was dashed by the coronavirus.

The swim took almost 12 hours, much longer than Clarke had predicted.

He said the rebounding swell of the headlands along the route, including at Redhead bluff, Merewether and Strzelecki, and a southerly current had made the marathon much harder than he had anticipated.

A shoulder gave out at one point, forcing him to swim mostly one-armed for a while, and he started feeling the cold down the stretch, but he held on to complete the swim in 11 hours and 53 minutes, having entered the water beside the Catherine Hill Bay jetty at 6am.

"I never felt like pulling out. A couple of times the shoulder sort of failed on me. It was just tough," Clarke said.

The swim had raised $13,000 by the time he stepped out of the water looking remarkably robust.

He completed media interviews on the beach and downed a swig of champagne before friend and former Knights captain Paul Harragon presented him with a commemorative trophy.

The first 22km of the swim took Clarke six hours, putting him on track to finish well before sunset, but the last 14km proved brutal. In the end he finished just 15 minutes before nightfall.

Clarke had been training for two-and-a-half years, swimming 100km a month, in readiness for the Channel swim before realising at Easter that he would not be able to travel to Europe.

He quickly turned his attention to a new challenge, a swim he dubbed "Coals to Newcastle" in honour of the historic shipping route between the Catho mines and the port.

He quit his job and moved back to Newcastle, training specifically for the ocean swim, a venture his mates at Swansea-Belmont surf club thought he was "mad" for attempting, given the distance and threat of sharks.

But he ploughed on, adding Beyond Blue as a charity partner then waiting for the right weather conditions in the same month he should have been setting off from Dover.

In fact, the Newcastle swim proved tougher in many ways than the fabled cross-Channel route. The water was only 16 degrees, two degrees colder than in the Channel this week. The buffeting of the headlands, unhelpful current and a 1.7-metre swell added to the difficulties.

"It was much tougher than I thought," Clarke said.

"I was feeling really strong getting to Redhead, but Redhead bluff really hurt bad. On high tide you had the tide really pushing back on that headland, and the sweep that was coming in.

"I had waves virtually coming three ways at me, but none of it going with me. When you're in that you've got to change your stroke, really punch into it to get going. That's where the body really hurts.

"The frustration and soreness was pretty high through there.

"Then Merewether was really tough, then Strzelecki and The Hill was really tough as well."

READ MORE ABOUT CRAIG CLARKE'S INSPIRING STORY HERE

The former national surf lifesaving champion had been in a buoyant mood when he spoke to a boatload of journalists off the coast of Redhead about midday.

He took a drink from a jerry-rigged bottle pressed into a hole in a foam kickboard then swam casually to the media boat, telling reporters he had "picked the right day".

But it all went south from there.

"We were on track at Redhead at midday. We should have been four odd hours [to go], but it's taken almost six," he said after arriving at Nobbys.

"I apologised to the support crew for some colourful language I called out a few times."

He said the Blacksmiths to Redhead stretch had been a "dream", but "a lot of the rest of it was bloody tough.

"Next time I think I'll just do laps between Blacksmiths and Redhead."

Clarke paid tribute to his support-boat crew, Lake Macquarie council lifeguards accompanying him on jet skis and onlookers who took up vantage points along the coast.

"That was a great boost, knowing there was so much support right along the course," he said.

"Knowing there were so many people behind me was a massive lift. It was a great day."

A small group of onlookers watched Clarke's progress from on high at Dudley.

"We can see them - going great at Dudley - well done," Harragon's wife, Pam, wrote on Facebook as Clarke passed by.

Covered in wool fat, petroleum jelly and sunscreen, Clarke had started the swim on a cold spring morning.

With the mercury hovering around seven degrees and the water temperature at 15, Clarke smothered himself in the "Channel grease" he had cooked up on his kitchen stove, gave a brief wave and "thanks, everyone" to a small crowd of friends and media shivering on the sand then slipped into the surf beside the jetty at 6am.

Clarke told the Newcastle Herald before setting off that he had not slept long but did not expect that to be a problem before the gruelling endurance test.

"Probably only four-and-a-half hours," he said.

"I was asleep at 9, but I woke up at 1.30. I was just lying there after that and eventually got up at 3. Adrenaline kicks in now."

Harragon said he admired his long-time friend's ability to adapt after the disappointment of missing out on the Channel swim.

"His brain was so hard-wired with attempting that goal, when it got taken away he just had to replace it with something," the former NSW and Australian prop said.

"In my mind this challenge is superior in certain ways. There's so much wildlife out there, meaning sharks, and swimming so wide [of the shore].

"His effort today is synonymous with Newcastle and the surrounding areas. We're tough, strong-willed people.

"To do 36 kilometres is beyond my capacity to comprehend."

Clarke's fundraising tally stood at $17,200 by 8pm.