For Richard Williams, outdoor swimming was more than just an activity - it was a turning point in his battle with depression.

"It has completely changed my life. I'm swimming twice a week, and in a cold tub every day. So I've gone from a recovering alcoholic and recluse, into firing on all cylinders now, and wanting to help others and spread the word."

Richard, who struggled with depression and anxiety for years, took part in the trial phase of the OUTSIDE study last year, led by Sussex Partnership NHS Foundation Trust and the University of Portsmouth, UK. It is first large-scale clinical trial to explore whether outdoor swimming can help reduce symptoms of depression.

“I was a person who could never actually go in the sea, even in the summer. But during the course and the training, you learn how to get past that initial shock and enjoy the euphoric feeling of being immersed in cold water.

“I've never been able to meditate properly or relax because there's so much going around my head, but in the water, it's just peace and you become more with nature. It has completely changed my life."

Now, researchers are expanding the study and calling for participants in 17 locations across England to take part in the next phase. Swimming sessions will take place in lakes, coastal areas and semi-heated outdoor pools.

The two-and-a-half year study, funded by the National Institute for Health & Care Research, will recruit 480 adults experiencing mild to moderate depression.

Participants will either take part in an eight-session outdoor swimming course alongside their usual care or remain in a control group receiving standard treatment. Researchers will assess whether swimming leads to a greater reduction in depression and anxiety symptoms.

Dr Heather Massey, from the University of Portsmouth’s School of Psychology, Sport & Health Sciences, is co-leading the study. She has been a keen open water swimmer for years, completing a number of long-distance events including a solo swim of the English Channel.

She said: “Participants in the outdoor swimming group in the trial reported reductions in depression and anxiety, with some also showing decreased use of antidepressants and sleeping tablets.

"Now, we need to see if these results hold true on a larger scale. If outdoor swimming proves to be an effective and cost-efficient treatment, it could become a widely available option for people managing depression.”

Before the pandemic, the number of adults experiencing moderate to severe depression in the UK was one-in-10. This doubled, to nearly one-in-five between March and June 2020.

Outdoor swimming has gained popularity in recent years, with anecdotal reports suggesting benefits for mental health and wellbeing. Previous research by the University of Portsmouth team found that regular open-water swimming may improve mood and overall wellbeing.

Clara Strauss, deputy director of research at Sussex Partnership and professor of clinical psychology at the University of Sussex, said: "This is the first large trial of its kind that will tell us if outdoor swimming is helpful for people living with depression.

"If it is, this could increase the range of options available to people as they find their path to recovery."

Hannah Denton, consultant counselling psychologist at Sussex Partnership NHS Trust, added: “This research could provide vital evidence on how outdoor swimming affects mental health. If it proves beneficial, we hope it will lead to more opportunities for people to experience the benefits of cold-water immersion.”

Each course can accommodate up to 10 people, and places will be allocated on a first-come, first-served basis. Participants will undergo medical screening before taking part, and trained medics will be on hand to ensure safety.

Anyone interested in taking part in the study can find out more and register their interest here: https://outside2.co.uk/

Studies are taking place at the following locations:

• Taplow Lake, North Maidenhead
• Chalkwell Beach, Leigh-on-Sea, Southend
• West Country Water Park, Bristol (ethnic minority women only)
• Avon Beach, Christchurch
• Roker beach, Sunderland
• Rayrigg Meadow, Windermere -lake
• Ilkley Lido, Ilkley
• Whole Health Swim Village, Colwick Country Park, Nottingham - lake
• Jesus Green Lido, Cambridge
• Quay Lake, Camberley,
• North London - West Reservoir, Woodberry Down, Hackney
• Loddington Farm Lake, Maidstone (Military Veterans only)
• Widewater Beach, Shoreham, Sussex (men only)
• Lymington Sea Baths, New Forest, Hampshire
• Gyllyngvase Beach, Falmouth, Cornwall
• West Kirby Marine Lake, Wirral, Merseyside