Go wild in the water and enjoy the great outdoors

But the proliferation of indoor pools, plus fears over pollution, sank open water swimming almost without trace. Now the combination of a best-selling book: Wild Swim by Kate Rew, a number of record-breaking swims and a desire to combat sedentary work with something physical, uplifting and outdoorsy, has led to a renaissance.

The activity, practised by a hardy few or superfit triathletes, is becoming more mainstream, according to Sarah Tunnicliffe, the Outdoor Swimming Society regional representative for North Yorkshire and the Lake District. Sarah, whose day job is working for English Heritage, says: "There are definitely a lot more outdoor swimmers.

"Anyone who swims will tell you that it makes an enormous difference to your mood. The physical benefits are huge and it's so therapeutic. There have been studies to show that regular swimming can help those who suffer from depression because it releases endorphins and I think swimming outdoors amplifies that."

Sarah learned to swim at Keighley baths but also enjoyed outdoor swimming as a child growing up in Cross Hills, near Keighley. "My parents used to say I had anti-freeze in my blood," she says. They had a point. Open water in this country is usually very cold, but there are ways to combat this.

You can gradually acclimatise yourself with short dips and you can wear a triathlon wetsuit, (made for swimming as opposed to a surf suit), which will extend the time you spend in the water. Having a positive attitude helps, as does running straight in rather than slow immersion.

"It gets easier the more you do it and it's very refreshing. Some people wear wetsuits, I don't, I like to feel the water," says Sarah, who joined the Outdoor Swimming Society when it was launched by Kate Rew four years ago, and now swims al fresco three times a week and twice a week indoors.

Other fears surrounding open water include the risk of drowning, being out of your depth and not being able to see the bottom.

"It's the fear of the unknown but once you've conquered those fears and got used to the cold it's very liberating.

"You're out in the fresh air and much closer to nature, with wildlife all around you and light shimmering on the water. It's just wonderful and, for some reason when you get out, your skin feels incredibly soft," says Sarah, who helps organise social swims for veterans and for beginners.

"What I really love about the social swims is that they're not competitive and there's a wonderful inclusivity. There are lots of different people in every age range. We have children with their parents and people in their late 70s and you don't have to be the best swimmer in the world to give it a go."

The interest in wild swimming has also been fuelled by a number of high profile record-breaking swims.

Eilidh Macdonald is the first person to swim the Little Minch – a much-feared Scottish sea crossing with treacherous currents.

The 22-year-old, who grew up in Tadcaster, swam the 15-mile stretch from Skye to Harris in just over nine-and-a-half hours in June after a year of training.

The Little Minch is considered harder than swimming the Channel, which was Eilidh's first choice.

"I felt unfit after leaving university and I wanted a challenge. My first thought was to try the Channel, but it was so expensive. Paying for support boats, equipment and registering for it brought the cost to 2,000. I was already 20,000 in debt from university, so it was a non-starter," she says.

Her uncle Murray, who lives on Lewis, suggested she try the Minch and said he would man the support boat, while her grandfather agreed to be on-board doctor. That was last summer and while working as a teaching assistant in Newcastle during her gap year, she started training for the charity swim

Her technique had already been honed by competing for York Swimming Club as a child, so she began by joining the Whitley Bay sea swimming group.

"I admit I was nervous because I was scared of not being able to see the bottom, but I soon got over that. The worst thing was the cold," says Eilidh.

"It's very icy in the Minch, so I practised in the sea. I had to give that up between September and April but I took cold showers instead of hot ones and used to dread washing my hair."

She also exercised for nine hours a week with a combination of running, pool swimming and cycling. And she stopped drinking for the last two months of her training.

"I tried to bulk up too, so I could keep warmer for longer, but no matter how much I ate I couldn't get bigger," she says. On June 3, and still a svelte size 10, she set off from Skye clad in a hooded wetsuit. After every 20 minutes of battling cold, strong currents and jellyfish, she trod water while re-fuelling with sports drink.

But she was shivering so much she could barely swallow. After 40 minutes, she defied her grandfather's pleas to pull her out.

Excruciating cramp struck in both thighs after six miles but she insisted on carrying on. "I got into a rhythm, but the worst bit was the last mile. I put my face back in and swam. There were purple jellyfish everywhere and I was so miserable I felt like crying. My family kept urging me on, saying: 'you'll regret it if you don't touch land'. I was barely conscious when I did."

Afterwards, she was elated, though there were a couple of unpleasant side effects including sunburn on her face around the googles – and an alarm when bits of her tongue began to fall off.

"No-one had warned me about the tongue. I imagine it must have been the salt," she says. Her tongue has healed and she has raised about 3,000 for charities, including the Martin House Hospice. Her feat has also turned her on to the benefits of wild swimming.

"I went back swimming in the pool, but it felt too hot and claustrophobic," says Eilidh.

"After swimming in open water, you feel so clean and refreshed."

If you fancy giving it a go, remember that a swimmer is about 20 per cent less efficient in open water than in a pool because of the choppiness, currents and cold. As for equipment, all you need is a costume, goggles or mask, a towel, a brightly coloured swimming hat, plus warm clothes and woolly hat for afterwards. It's an inexpensive sport, especially given that entrance is usually free. Sarah Tunnicliffe's favourite Yorkshire swimming spots include Malham Tarn:

"It's one of the highest tarns but it's quite shallow in places and the views are beautiful."

She also loves the coast off Sandsend: "It's very invigorating – the coastline is beautiful there. Swimming out and getting that amphitheatre view back into the land gives you a different perspective."

Outdoor Swimming Society founder Kate Rew also lists Stainforth Force, Thornwick Bay and Semerwater in Yorkshire, though her favourite swim in Britain is in the Fairy Pools on the Isle of Skye – a series of crystal clear river pools. "They all offer a different experience, unlike a swimming pool," says Sarah.

"Outdoor swimming is magical, totally invigorating and it somehow makes you feel free, more alive and more appreciative of the beautiful country we live in."

Best reads: Wild Swim by Kate Rew (Guardian Books 12.99) and Waterlog – A Swimmer's Journey Through Britain by Roger Deakin (Vintage 8.99)

Best website: Outdoor Swimming Society, www. outdoorswimmingsociety.com

Best outdoor swimming holidays www.swimtrek. com

OUTDOOR SWIMMING SAFETY TIPS

Never swim alone.

Make sure you can get out as easily as you got in. Plan easy entry and exits

Know your own ability.

Stay within 100 metres of the bank or shore unless you have a boat escort

Never underestimate the strength of currents.

Don't swim in reservoirs. It is prohibited, they are too cold and too deep and automatic suction systems can create downward currents.

Wear a brightly coloured silicone swimming hat so boats – or rescuers – can see you easily.

If sea swimming, be aware of tides.

Avoid swimming near blue green algae and do not swim with open cuts or you may contract Weil's disease

If in doubt, stay out.