Watch Jacquie Bird's report
Former Royal Marine Commando and triple amputee Mark Ormrod is preparing to swim from Plymouth's Drake's Island back to the shore for charity.
His swim to Devil's Point is part of a fundraising challenge which he hopes can pass £400,000.
Speaking after his final training session, Mark said the conditions were understandably tough.
He said: "The tide was, it felt like you could feel it under the water pulling you and twisting you and there was one point when I was swimming and I looked up and I was facing completely the wrong way."
As part of his training for the event, Mark has been coached by fellow Plymothian and Olympian Sharron Davies.
He has persuaded her to travel from her home near Bath on Friday to swim with him - her first proper sea swim since she was 11.
Sharron said: "I am the world's worst swimmer in cold water. I am totally and utterly allergic to it. I only ever go into 80 degrees and I get Reinards as well, where you lose the blood from your fingers and toes. So I am a little bit worried about it. And it would be really embarrassing wouldn't it, if this amazing athlete, but with only one arm, has to save an Olympian because I can't swim."
Former Royal Marine Mark lost three limbs when he stepped on an improvised explosive device while on foot patrol in Afghanistan in 2007. Five months later he walked on artificial legs on the parade ground to receive his tour medal with his fellow servicemen.
His determination and drive have seen him take on many challenges. He is a multi-medal winner at two Invictus Games, has written one book with another on the way and a feature film is in the pipeline.
This challenge was started to raise money for a military charity he is Trustee for, Reorg. It uses Brazilian Ju Jitzu to help support servicemen, veterans and the emergency services.
Mark set himself the challenge this year to raise £1,000 by shaving off his beard, but the fundraising went crazy, so he pledged to run 5k and footage of him falling and getting himself up again went viral.
So far he has raised more than £270,000 and is hoping the latest challenge on Friday 28 May will take him over £400,000.
"I had a very small ambition and you know the money would have been great but what I really wanted to do was get eyes on the website so everyone could understand the mission of what Reorg were trying to achieve," he said.
"This has just blown up and this is what it's about, it's about community. Getting people together with a shared passion, who, in a nice way, go through shared hardships and that's what brings them together and helps them with any issues they do have."