The UN’s Patron of the Oceans has just three miles to go to Shakespeare Beach, the traditional starting point for cross-Channel swims to France.
He will become the first person to swim the 350 miles from Land’s End, wearing only Speedos, goggles and a hat.
He’s taken half a million strokes, burned 98,000 calories and been stung by countless jellyfish.
Lewis said: “I’m mentally, physically and emotionally exhausted. I have never done anything so tough in my life.
“But we are also excited. We can see the white cliffs of Dover and we are going to get there.
“It has been incredibly tough, especially when we were trying to get around Dungeness and we couldn’t several times.”
Lewis has been campaigning for 30% of the world’s oceans to be protected from damaging exploitation such as industrial fishing, mining and drilling.
He is angry that waters set aside as conservation zones in the UK have little protection.
Goodwin Sands, near Dover, was given protected status by the government on World Oceans Day in June.
The shallow gravel bank is an important habitat for sand eels, blue mussels and the rare Thornback ray. It’s also one of only two haul-out sites in the south east of England for seals.
Yet, Dover Harbour Board will be allowed to dredge 3m tonnes of aggregate from the area to expand the port, tearing up the seabed that supports such a complex web of life.
Joanna Thomson, who runs the campaign group Goodwin Sands SOS, said: “If we don’t stop the dredging now there will be nothing left.
“All the creatures are in the sand and is you start taking the top two metres off the sand there will be a huge ecological impact on the rest of the area.
“I know we can’t see it and out of sight out of mind, but they are there.”
The Port of Dover said Goodwin Sands is the closest and most economic source of aggregate for construction work in the Western Docks, expansion which will increase trade and jobs.
The independent regulator, the Maritime Management Organisation, ruled that the dredging wouldn’t “hinder the conservation objectives” of the protected area and gave the port the go-ahead to start removing aggregate from September next year.
But Lewis called on Environment Secretary Michael Gove to intervene.
He said: “Goodwin Sands is a perfect example of what I’m fighting for. It has been recognised for its biodiversity, its been set aside by government as a marine conservation zone and what we have is a company allowed to dredge the seabed and destroy the biodiversity marine life depends on.
“Why is it that the economy also seems to be more important than the environment?
“I’ll be asking the government to review this decision. If we carry on there’ll be nothing left for our children and grandchildren.
“It makes a mockery of marine conservation in the UK.”
He said the Goodwin Sands decision was only looking for short-term problems.
“What I’ve realised in 50 days of swimming is the depth of feeling about our oceans,” he said.
“I’ve received thousands of messages about the oceans, how important they are, how much they are changing by plastic pollution and over fishing.”
Lewis will reach Shakespeare Beach in Dover at 1.30pm on Wednesday and has invited members of the public to join him.