KEEP a look out at sea if you're on the beach between Bournemouth and Boscombe on Friday (August 31).

Because you may spot the remarkable Chris Larkin, battling through the waves, finishing his extraordinary fund-raising journey.

Chris, 59, who weighs around 27 stone, used to weigh more than 36 stone two years ago.

But that didn't stop him determining to raise money for Alzheimer’s Research UK in honour of his parents who both died with vascular dementia.

His effort is actually part of the charity's Running Down Dementia campaign, which challenges people to run 100km during the summer. However, as the grandfather-of-three cannot run due to a knee injury, he turned to swimming instead, using it as part of his mammoth effort to get fitter and lose 21 stone.

Chris began piling on the pounds in his mid-30s when his lifestyle became much more sedentary after taking on a new job.

“I was a very fit guy in my 20s and early 30s," he said. "I ran a marathon, I used to run five miles every other day, I would cycle 25 miles at weekends and played squash regularly. But I never ate well, I’d eat whatever I wanted."

After the stopped exercising he started to put on weight. "I didn’t notice it at first, but over a long period the weight piled up," he admitted.

“I’ve made a lot of progress with losing weight and had lost over 10 stone, but in February I injured my knee and got arthritis," he said. "That really set me back and I got depressed about it. I had a dream of running a marathon, but that’s not going to be possible now."

After seeing Running Down Dementia on Facebook he decided to swim his miles.

Chris, who lives in Swansea, began the challenge at the end of May and originally targeted 100km, but he has now upped his target by 30km and for the final 2km hopes to swim in the sea from Boscombe Pier to Bournemouth Pier on Friday.

"My dad died in 2013 and then not long after his funeral my mum went downhill and we realised we were going through the same thing with her," he said. "She died last year. They were wonderful people, but my memory of them is clouded by the last few years of their lives, it was so undignified.”