The latest fitness trend and fashionable Scandi import is the “swimrun”, a fusion of cross-country running and open-water swimming — essentially a triathlon without the cycling. Originating in Sweden, it is gaining converts here, with thousands of people set to take part in the UK this year.

With its emphasis on experiencing nature “in the purest possible way”, with “respect for yourself, for others and for the environment”, the swimrun’s Scandinavian roots are very clear. It was created by a group of Swedes in 2002, when four friends pledged in a drunken bet to race in pairs from Uto to Sandhamn, islands in their country’s archipelago, with the losers picking up the hotel and bar tabs at the end.

By 2006 it had grown into a commercial event (which takes part across Europe) that is still known as the Otillo — which means island to island — in which entrants cover 6.2 miles by swimming and 40 miles by trail-running, with each discipline broken up into bite-sized (ish) chunks. Pippa Middleton and her brother, James, were one of the teams that took part in 2015.

If this sounds like the kind of challenge for you, then you are in luck. Over the summer months you can swimrun in the Lake District, where the Breca Buttermere event offers eight swims and nine runs across the fells and includes a 1,900m (6,200ft) ascent; or in the Norfolk Broads, where you can opt for a gentle introductory course involving 1.9 miles of swimming and 6.2 miles of running. And Great Swim, Europe’s biggest open-water swimming series, recently announced the launch of its “ Great North Swimrun” over three distances — short (6.6 miles total distance), middle (13.2 miles) and endurance (22.7 miles) — taking place at Lake Windermere on June 10.

“We realised that people want something different,” the Great Swim organiser Alex Jackson says. “And the ethos of doing it in pairs and exploring previously inaccessible terrain is really capturing people’s imagination.”

Clearly there is demand for a sport that shuns smooth tarmac surfaces and carefully measured courses in favour of off-road tracks, stunning scenery and an element of exploration. It has other benefits too. “The swimrun is much more accessible [than a triathlon] to a lot of people because you don’t need a bike or any major equipment other than a wetsuit,” says Alan Anderson, one of a group of triathletes who brought the swimrun to the UK. While on a night out in 2015, he and a group of triathlete friends challenged each other to a swimrun across Loch Lomond and its 12 mini islands. That ultimately led to the country’s first official swimrun last year.

Anderson explains that “triathletes can spend ridiculous amounts of money on bikes and accessories. It’s become a rich person’s sport”. By far the biggest swimrun outlay is the race entry, which is usually about £100 for each team of two, although there are plenty to choose from, with more shorter, cheaper options becoming available. In addition to the Loch Lomond event, first staged in September 2015, Anderson’s company, SwimRun UK, is holding races in Snowdonia, Glencoe and Majorca this year, with more venues being added.

Swimrun distances are not standardised but typically the Norfolk Broads event would constitute a short course; the longer, more extreme courses involve a swim of about 5 miles and a run of anything from 15 miles to more than 25 miles (in comparison, the shortest “super sprint” triathlon is a quarter-mile swim, 6.2-mile bike ride and 1.6-mile run; a long-distance, or ironman, triathlon is a 2.4-mile swim, 112-mile bike ride and 26-mile run).

It’s more accessible to a lot of people because you don’t need a bike or any major equipment other than a wetsuit

The runs and swims are broken up, so you could be in and out of the water more than ten times; each swim could be anything from 150ft to a couple of miles. Some of the longer distances sound intimidating; however, swimrun is a more attainable goal than a full triathlon because there are only two disciplines to perfect, so training time is shorter.

Anderson, a stand-up comedian who describes himself as a “keen but rubbish” triathlete, says that swimruns are attracting as many serious but bored triathletes as complete beginners. “It’s not an easy option,” he says. “In many ways it’s harder than conventional endurance events because the terrain is tricky and you need to adapt to the ever-changing environments.”

Unlike triathlons and aquathlons, there is an unpredictability to the format in that the disciplines are repeated, rather than being completed in distinct stages. “Breaking the swims and runs up into manageable bursts brings a short, sharp nature to it,” Jackson says. “Psychologically and physically people like the idea that they don’t have to cope with one huge slog of a swim or a run.”

Then there is the additional challenge of not being able to change your clothes. Triathletes tend to wear a wetsuit that they remove after the swim, then put on trainers for the run, whereas the rules of swimrun state that competitors must wear a wetsuit and carry certain safety items or flotation devices from start to finish. This means swimming in trainers across cold tarns and running in a wetsuit and soggy footwear between the stretches of water. Many regular swimrunners have taken to wearing short wetsuits that leave the lower legs free for running and pair them with knee-length compression socks that offer protection from brambles and heather.

As the sport has evolved, so has the imaginative use of ever more quirky equipment, such as football shin pads to aid flotation, and trainers with holes drilled into the arches — not the soles, I am told — to allow for better drainage as you switch from water to land.

It speaks volumes about the emergence of swimruns as a trend that clothing manufacturers are beginning to design equipment for participants. A recently launched swimrun-specific shoe, the Primus Trail Soft Ground (£110, vivobarefoot.com), promises to be “quick draining, for minimal wet weight” — or less soggy feet when you run. “You become obsessed with things like this when you swimrun,” Anderson says. “You are constantly looking for socks that don’t hold water.”

For the thousands aiming to dip their trainers into swimrun waters for the first time this year, Anderson advises a shift of mindset from anything they have previously tried. “What it removes is the constraints of other activities,” he says. “I’ve swum in Loch Lomond for years, but only in sections of it. By swimrunning we can access parts of the coastline that we thought were completely out of bounds. It offers an exceptional type of freedom.”

The top swimruns this year

Great SwimRun (greatswim.org/swimrun)
Date: June 10
Entry: £150 (short) to £300 (long) per pair
Perfect for beginners, this Lake Windermere event has 6.2-mile, 13.2-mile and 22.7-mile courses.

Glencoe Skyfall (swimrunuk.wordpress.com)
Date: June 25
Entry: £100 (short) to £150 (long) per pair
Held at the foot of Glencoe this involves running across some of Scotland’s highest and most remote moorland. There are three distances to choose from.

Love SwimRun Holy Island, Anglesey (loveswimrun.co.uk)
Date: September 23
Entry: Solo £95; pair £190
The longest run in this 11.4-mile event is 3.5 miles and the longest swim half a mile. It crosses the beautiful Holy Island and requires rock-hopping across sandy bays and traversing cliff edges.