Cold water dippers take a dip in the sea. There are about eight men in the water, some are wearing swimming hats and they are all topless.
Garry Owen
BBC News
Many people swear that cold water swimming has a positive effect on their mental health and wellbeing.
Now research is being done to see if there is science behind the theory that taking an ice-cold dip can help tackle post-traumatic stress disorder (PTSD).
Researchers will test swimmers' saliva to track cortisol levels - a stress-related hormone - before and after cold water immersion.
Denise Hill, who is leading the study, said her research was a UK first and wanted to test if cold water dipping could be used as a "supplementary" treatment for people with PTSD alongside talking therapy and medication.
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Figures suggest that about one in 10 people in the UK will experience PTSD and the NHS estimates it affects about one in three people who have a traumatic experience.
It can be caused by car crashes, violent assaults, health problems and conflict, which is what caused military veteran Phil Jones's PTSD.
The 42-year-old former Royal Marines Commando admitted sometimes "motivation can be quite hard" and he "can feel quite negative".
He said: "Cold water immersion has been a game-changer for me. I don't like getting into the water but I know it's good for me.
"Coming out of the water you're absolutely buzzing. I feel happier, more focused, more motivated and problems tend to wash away."
Phil, who has seen action around the world as a landing craft coxswain and hovercraft pilot for 45 Commando, was part of a small group of military veterans helping academics from Swansea University in what they describe as a ground-breaking study.
Researchers monitored cortisol levels of the volunteers before and after they took dips in the chilly sea off the south Wales coast.
Before the research started, swimmers gave saliva samples four times a day over two days.
Phil Jones walking out of the sea. He has black shorts on with a red and yellow stripes. He has black gloves on. He has tattoos on his chest and arms. And has people behind him in the sea.Swansea University
Then, after each 10 minute weekly cold water session, dippers gave more saliva samples and do a post-swim questionnaire assessing their levels of wellbeing, depression and PTSD symptoms.
Researchers were planning to take blood samples of swimmers in the next stage of the trials and interview participants about their experience before any clinical trials begin.
"There's growing research that the impact of cold water immersion has on mental health conditions," said Dr Hill, an associate professor in sport psychology at Swansea University.
"But surprisingly, no study has looked at the specific impact of cold water immersion on PTSD."
She said the study was a "first and small step, but an important step" into whether cold water immersion could help ease the symptoms of PTSD.
Denise Hill at the beach. She is wearing a black dry robe with a blue lining. She is also wearing a blue hat. She is smiling at the camera.Swansea University
Dr Hill said her research team wanted to find out if cold water dipping "can be used as some kind of supplementary therapy if there's a diagnosis".
"Of course there's talking therapies and medication," she added. "But we are looking to see whether cold water immersion can form part of that treatment package."
The Bristol Channel is about 9C (48F) when Phil and his friends from the military veterans group go for a session at Caswell Bay on the Gower Peninsula.
"I've been doing it for about five years and it's been a mainstay in keeping my mental health in check," he said.
Former Welsh guardsman Tony Davies also said he felt "invigorated".
"It makes you feel so alive and clears your head for the rest of the day," he said.
Wales' veterans' commissioner Col James Phillips is also supporting the research.
"Without the evidence and data, it is very hard to argue for resources and specific services," he said.
Related topics
Wales
Open water swimming
Mental health
PTSD