Late on a snowy Stockholm morning, eight colleagues file down from their office to a small jetty on a nearby lake, change into swimsuits and, one after another, step through a small hole cut into the ice.

For the hardy friends, this pre-lunch dip has become a weekly work ritual - come rain, sun or snow.

At the saltwater Brunnsviken lake, they submerge themselves into the 0-degree Celsius water for a few seconds each, to the cheers of their friends before leaping out and wrapping up in bathrobes. 

Some gasp as they step down a small ladder, surrounded by the snow-covered ice covering the lake. Others yelp, and two of them dunk their heads under the water before heaving themselves out.

The group, aged between 34 and 61, started out in 2017 in a bid to beat the post-holiday blues when some friends, all colleagues in the marketing department of a company in the suburbs of Stockholm, proposed a swim one lunchtime.

"We started going swimming in the summer when it was lovely and warm, and we thought 'We wonder how long we can keep doing this?'," said Karin Wallford, a member of the group, wrapped up in a woolly hat and thick coat after she took her icy dip.

But the group, which is usually between six and eight swimmers, kept up their weekly swims even as the biting Swedish cold set in and ice formed on the lake — and even enjoyed it.

"It feels like you have, in some way, rebooted your mind," said Michael Porselid after his swim.

The group was forced to take a break last winter when ice on the lake, which feeds into the Baltic sea, became too thick to cut in February and March.

But this year, the colleagues plan to enjoy their ice-dip no matter how cold it gets, using saws, snow shovels and branches from the trees lining the lake to open a hole in the ice to keep on swimming.

"I’m quite nervous, but when I finally do it I'm so happy I went," said Annica Gunnrin, energised after her swim and dressed against the cold again.

"I never regret going swimming."