The path to the water is treacherous. The snow has covered the ice making it slippery underfoot. It is 7.45 am and dark, but my friend Vicky and I have head torches and the moon is bright.

Our walk – prior to lockdown 2021 – is through the woods and down the path to the edge of Threipmuir reservoir in the Pentland hills, just south of Edinburgh. It is impossible to tell where the water starts as everything is covered in a thick layer of snow. And the snow is also coming down in earnest, landing on our eyelashes and into our dry bags, as we unpack and start to undress.

Once stripped to our swimsuits, neoprene boots, gloves and woolly hats, we approach the ice. A pickaxe makes little impact to begin with, but we continue with one of us using the axe while the other smashes away with boots and moves huge chunks of ice with our hands. It is quite a workout and seems so ridiculous that we laugh until we have tears rolling down our faces.

• Preparation is key as ice-bathing can potentially be a dangerous pastime in the UK, as we don’t have places, such as Finland, where there are 260 winter-swimming centres, which often include changing facilities and saunas – as well as specific entry and exit points in the ice. 

• Ice-bathing must always be approached with caution, never alone, and having risk assessed the location first. Acclimatise to cold water carefully, keeping your dip short and warming up quickly afterwards with layers of clothes and a hot drink. 

 • Going in to very cold water (typically less than 10C) can cause numbness and pain, particularly in the extremities, such as the hands and feet. Neoprene socks and gloves can help protect hands and feet. 

• The Outdoor Swimming Society has tips on how to acclimatise to cold water

After about five minutes, we start to make headway, working as a team to create a little plunge pool. When we visited two days previously we were able to clear a long swimming channel, but today the ice is too thick. A flock of Canada geese fly past, skimming the top of the ice, and a bullfinch hops around the shoreline, its pinkish plumage the only colour visible in this white landscape. Finally, we have cleared enough ice to swim.

Preparation is key as ice-bathing can potentially be a dangerous pastime in the UK, as we don’t have the infrastructure of places such as Finland, where there are 260 winter-swimming centres which often include changing facilities and saunas – as well as specific entry and exit points in the ice. Here, we often need to look to more remote spots in order to find ice, which adds a huge element of risk to the process.

It must always be approached with caution, never alone, and having risk assessed the location first. Acclimatise to cold water carefully, keeping your dip short and warming up quickly afterwards with layers of clothes and a hot drink.

I lower myself down into the 0.8C water until my shoulders are beneath the surface, and try to calm my breathing and bring my heart rate down as I absorb the shock of the cold. Even though I have swum through four winters, my body’s automatic response to the extreme cold is still powerful.

I try to remain calm, swimming a few strokes and trying to avoid the ice shards, which can cut. Despite having gloves and socks, my fingers and toes are are numb, my body sending all available heat to my core. I feel utterly alive and exhilarated, though. But there is a fine line between fun and hypothermia, so we tear ourselves away as the dawn light turns the mountains pink. Beginners should stay in the water for two minutes maximum.

Then it is a race to warm up, using cold, muddled fingers to put socks on top of socks and more layers than you imagine possible, pouring hot drinks from flasks, doing star jumps and squats to get the body warmed back up. Though the massive rush of energy and unbridled joy far outweigh thoughts of frozen toes.

As we are packing up to leave, we hear belly laughs and people approaching through the snow, and then encounter three women armed with an axe and a rolling pin to continue what we started. As the hilarity of the moment hits them, Wendy Masterton tells us: “We’ve been cold-water swimming with ice around the edges before but this is the first time we’ll actually experience breaking the ice in order to get into the water.”

Outdoor swimming has seen a dramatic rise in popularity over the last year. As swimming pools closed due to Covid restrictions and holidays were cancelled, many people turned to their local beach, river, loch or lake to swim. And many have continued, despite the reopening of some pools during summer and early autumn. The Outdoor Swimming Society (OSS) has seen website traffic increase by 46% to 785,000 unique users and membership increase 36% to 136,000; its Facebook group has grown by 73%.

In addition, local wild swimming groups have reported to the OSS growths in membership of their Facebook pages of between 50% to 500%. Open water lakes are also reporting a huge increase in visitors .

“Outdoor swimming is now part of the UK psyche, part of our love of free-spirited adventure,” says OSS founder Kate Rew. “People are looking for exercise and adventure closer to home, thousands have made this their time to embrace rivers, lakes and the sea. For some, it is about self-sufficiency and stoicism: the perfect activity for a life under the pressures of a pandemic. I think others are winter swimming to achieve a high that we can’t get anywhere else right now.”

A study by Dr Chris van Tulleken and Dr Mark Harper, published by the BMJ, discovered that “regular open-water swimming results in a post-swim ‘high’, triggered by the release of beta-endorphins, dopamine and serotonin. Furthermore, facial immersion in cold water stimulates the vagus nerve, resulting in an anti-inflammatory response.”

Ice swimming, once only attempted by a few hardy souls, has been dominating Instagram feeds this winter as more swimmers seek out the extreme cold. Claire Williams began outdoor swimming at Wardie Bay, Edinburgh, in May after losing her mother to dementia

“Outdoor swimming has helped me massively, the people I’ve met, the friends I’ve made and also just the peace I’ve found from being in the cold water,” she says. “With the new research suggesting cold-water swimming wards off dementia, I will never ever give it up. I only wish my mum had been around to enjoy it with me.”

Cassandra Barron had her first ice swim at Threipmuir reservoir earlier this month after taking up swimming in the sea at Wardie Bay during the spring lockdown.

“I have swum every day in January so far and wanted to push myself further so I had my first exhilarating ice-swimming experience this week,” she says.

In Scotland [as in England], we are still able to exercise outdoors within our local area with one person from another household, so outdoor swimmers who live near water are able to meet with another person during this time, providing a lifeline for those who swim to help deal with the stress of the pandemic.

It might be extreme but immersing yourself in icy water is a wonderful way to fill up with endorphins, get a nature fix and have a thrilling adventure without having to travel.

• The OSS’s tips on acclimatising to cold water

Taking The Plunge by Anna Deacon and Vicky Allan, is published by Black & White publishing. Follow Anna on Instagram at @wildswimmingstories