A Pembrokeshire man is raising funds for Cancer Research UK.
Lee Burton, from Narberth, was diagnosed with prostate cancer a couple of years ago.
This led to an operation for its removal.
The cancer was then found in a lymph node, for which Mr Burton said he was given 'massive doses of radiation' through radiotherapy.
Mr Burton said: "After having surgery to remove cancer from my body, I decided while having the follow-up radiotherapy, I’d get stronger, not weaker, so started swimming.
"I would like to make some effort to raise money in a small part to contribute to the organisation that treated me.
"I know it’s the NHS and we’re all paying for it, but there is little doubt that Cancer Research is an amazing organisation and needs all the funds we can spare.
"So I will not just swim 10km in November but will swim a minimum of 40 kilometres."
Mr Burton said that when he found out he needed radiotherapy, he decided to get fit beforehand and started swimming, gradually working up to swimming a mile every weekday.
He said: "Recently, I started a swimming challenge of 10km in November to raise money for Cancer Research and the sponsorship is flooding in."
Sponsors can visit https://fundraise.cancerresearchuk.org/page/lees-giving-page-3112547 to donate.
"Today was day eight of my 2km per day goal.
"My intention is not only 10km but 40km for which I’m well on my way."
At the time of writing, Mr Burton has raised £870 with £175 in Gift Aid.
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