YESTERDAY I went into the North Sea, water temperature around 10 °C, dressed as a frog. This is not the first time I’ve worn something daft while wild swimming. There was, for instance, the alien squishy brain cap, worn for the “heads-up breaststroke with silly hat” race at the inaugural Scottish Winter Swimming Championships earlier this year, or the novelty Christmas headband donned in December last year and, perhaps most eyebrow-raising of all, the goose-bumped birthday suit worn at a 7am mass skinny dip at Wardie Bay, Edinburgh.

And I’m not alone. One of the characteristics of the community of people who like to take a dip in the coldest of waters is that they hardly need the slightest excuse or prompting to do anything silly or wear something ludicrous in the water.

This is one of the reasons that photographer Anna Deacon and me chose a fancy-dress swim as the launch event for our book, Taking The Plunge: The Healing Power Of Wild Swimming For Mind, Body And Soul. Wild swimming gatherings are Scotland’s eccentricity at its best – both delightful and a little bit radge. It’s the loony dook mentality taken to extremes.

So yesterday around 80 people turned up and dived into that chilly water. Anna came dressed as a caught fish. One person came as Neptune, another as Ursula the sea witch. Ice swimmer Gilly McArthur had travelled all the way from the Lake District to plunge into the sea while wearing her “Baltic” hat. There was a very convincing jellyfish bonnet.

What’s striking about the wild swimming groups around Scotland is that so many of their gatherings revolve around some kind of daft mucking about – mass handstands, skinny dips, Easter bonnet swims, the so-called Fife salute (a baring of breasts while facing the paps of Fife), spontaneous post-swim conga dances. The year goes from one excuse to go into the water wearing something ridiculous to another. One would think that at times these adults were a bunch of kids. But often it turns out they’re serious people with difficult jobs – people involved in medicine, mental health, international conflict resolution, management consultancy. All throwing themselves into the fun.

This approach is particularly notable within our local Portobello swim group, The Wild Ones. They have, it often seems to me, a serious play ethos. On my first-ever night swim with the Wild Ones, one couple in their sixties started doing handstands in the black, dark water. Richard Cox, a determined seeker of fun, once told me: “This is grown-ups getting the chance to play with no rules, and this is so important in this target driven age in which we live.”

Sarah Morton, one of founders of The Wild Ones, observed: “We have always been about the fun – about doing handstands and silly synchronised swimming routines. The fact that we’ve kept that is really important to me, that it doesn’t get too serious.

“My dad swam and he has an amazing sense of fun. I always think about him when we’re doing all the fun stuff.”

Web developer Chris Booth said: “Within our group, it seems as if there’s a dimension of caring about connection and caring about the natural world, and a really strong sense of playfulness.

“We do all these mad things like pretend synchro swims. Handstands are really important. We’ve built up a kind of shared culture. For me, it almost becomes an act of defiance. We’re in this situation at the moment where we’re faced with so many dreadful things going on – the impending destruction of the world as we know it. And for me it’s a really radical act in the face of that to continue doing something fun and joyful and connecting with nature while we still can – and connecting to people.”

Our book is about how wild swimming is good for mental and physical health, and contains countless images and stories of people who have found relief from pain, depression, grief, anxiety and other troubles through cold water dips, as well as the latest research on cold water physiology. We include a whole chapter on play and silliness, since there’s no doubting it’s an element of why it’s good for us.

Is there a tiny bit of exhibitionism involved in swimming too? Perhaps for some, but it’s the kind of exhibitionism that is a finger up to prevailing body ideals and consumerism, that’s about allowing yourself to be a little ridiculous. As Anne Altringham, also a frequent swimmer with The Wild Ones, said: “One of the things that thrills me is seeing people’s faces when I tell them that I do it. It’s that something that is just a little bit transgressive.”

Many wild swimmers feel a little bit that way. But that’s not the only reason they’re in there. They’re there for the buzz the cold gives them. They’re in it for the mental health lift. But mostly they’re there for the fun.

The ice breakers. How Scotland's ice swimmers taught me to love the cold.