It’s official. The clocks go back this weekend, the days are about to get shorter and the mercury is plummeting faster than Ms Greta Thunberg’s mood when faced with a passing Mr Donald Trump. Autumn is here, and with it the very real possibility of the winter blues. For those of us residing in the northern hemisphere, a staggering one in three might succumb to varying levels of “winter depression”, the scientific term for which is, aptly, SAD – or Seasonal Affective Disorder.

That means: ever diminishing levels of energy, lower self-esteem, anxiety, a craving for all of the carbs (which naturally leads to gains of the less desirable kind) and the siren song of a warm bed. For a small percentage of us, the symptoms are so severe that we can’t even function or work properly. But what if there was a way to not only combat the effects of SAD, but to connect with the outdoors, and give your physical and mental wellbeing a much-needed boost as well?

It might seem counterproductive – OK, completely insane – to go swimming in cold water when the temperature outside is dropping, but for Mr Calum Maclean, a photographer, filmmaker and Outdoor Swimming Society ambassador, it’s a compulsion. “It’s a need,” says Mr Maclean. “I have to go swimming. I have to be in that cold water again, I want to feel that rush and that little bit of initial shock, followed by that ‘Yes!’ moment.

“Over winter I try and swim every single day,” he continues. “These swims are different to the rest of the year: they’re shorter, more mindful, more about the experience than getting exercise.”

With that in mind, here are five reasons why taking the cold plunge might be the best thing you do this season.

You wake up feeling groggy. You mainline caffeine to help you fight said grogginess. You get to work and autopilot your way through the day. Sound familiar? What if you could start your morning on a high – and ride that feeling for the rest of the day?

“What every open-water swimmer experiences is that chemical buzz from going into cold water,” says Dr Heather Massey, lecturer at the school of sport, health and exercise science at Portsmouth University. “Some people call it the post-swim high. You’ve got different hormones, chemicals and endorphins going on in your body, and they’re all having their separate effects: lifting your mood, making you feel quite alive.”

For Ms Karen Smith, the Outdoor Swimming Society’s swim champ coordinator, it’s the ultimate pick-me-up bar none: “I challenge anyone to be sluggish after dragging themselves to a body of cold water in the dead of winter and swimming, dipping, just getting in,” she says. “It will make you feel alive in ways you can’t even imagine.”

Wading into sub-20-degree water, in the dark, first thing in the morning, when you’re cold, is a challenge. A big challenge. “When I can see my breath in front of my face and I know that the water temperature will be sitting around one or two degrees,” says Ms Smith, “that expectation of what’s to come is really, really tough. It hurts at that temperature, like tiny little razor blades for the first few metres. But after that? Sublime bliss.”

If you can rise to that challenge, it’s not just the swim that feels good – everything else in your day becomes easy in comparison. “It’s getting over that mental barrier that really helps with forgetting any worries and having a sense of achievement,” says Mr Maclean. “After a swim, I worry a lot less. Whatever was taking me down is gone. Once I’ve fully recovered, it’s a calmness that lasts all day.”

We all know it now: too much screen time is detrimental to our physical – and mental – health. Even Mr Maclean, who lives in the Scottish Highlands resplendent with lochs, waterfalls and undulating peaks, has trouble. “Although I have great access to stunning swimming, I’m as guilty as anyone of being glued to my phone,” he says. “I find too much screen and sitting time dulls my brain, makes me unhappier and worse to be around.”

If you’re sick of spending your working day sat in front of a computer, and your evening scrolling through Instagram while binging the latest show on Netflix, what better way to ditch the digital than jumping into the sea, or a lake, or even a lido? “You’re taking yourself out of the built environment,” says Dr Massey. “It’s refreshing, it’s different, you’re not needing to interact with lots of screens. It’s just a relaxing thing to do, and because you’re relaxing, you’re able to not have the pressures we have in this modern day.”

Staying indoors in the colder months can lead to loneliness – which only compounds our winter blues. The antidote is to seek activities that build meaningful relationships and foster a sense of belonging. And cold-water swimming is one of the best ways to do exactly that. “Open-water swimmers are an inclusive, likeminded group of people,” says Dr Massey. “There are people of all shapes and sizes taking part – people that might not necessarily go into a pool because they might be conscious of being seen in the water.”

Ms Smith concurs: “I swim at Parliament Hill Lido in north London,” she says. “No matter what time of day I go, there are several people I know, and we always stop for a chat. It’s extremely community-minded. Many of the lifeguards have worked at the lido and ponds for years, and their children are lifeguards in the holidays – it’s like family.”

“Being out in nature is rewarding – something that’s been the focus of a lot of research,” says Dr Massey. “Whether that’s in the green space (trees and grass) or out in the blue space (in the sea or a lake) there’s lots of anecdotal evidence that suggests people’s wellbeing improves when they’re in the natural environment.”

When it comes to cold-water swimming, the range of picture-perfect options out there means you’re spoilt for choice. And for Mr Maclean, part of the buzz is in the adventure. “I always want to find new, interesting and beautiful places,” he says. “Ideally somewhere that takes some effort to get to, and away from roads, cars, man-made noises. Swimming under the huge ice slabs in Loch Coire an Lochain on the mountain of Braeriach in the Cairngorms was an incredible experience. I’d camped beside the loch for the night, as clouds whipped over the surface. Then as daylight came, I got in and swam! The water looks a very clean, clear blue colour and it was painfully cold – but the sheer exhilaration of the swim made me forget the cold quickly.”

_Cold-water swimming can result in serious complications if you have certain cardiac, respiratory or skin conditions. _

For advice on how to get started, visit  outdoorswimmingsociety.com