3 August 2010 Last updated at 08:05 ET

No diving? No bombing? No rules swimming

Columnist Matthew Parris has been called "ignorant" and his actions "dangerous" after swimming across London's River Thames. But up and down the country, people are dipping a toe in the trend for outdoor swimming, writes Tom de Castella.

It's a sultry July afternoon and about 30 bathers are floating, chatting and breast-stroking their way through the cool, green water. Oak trees, willows and birch overhang the pond, moorhens pick their way across the shallows and a flock of Canada geese swoops down overhead.

If it wasn't for the brightly coloured bikinis and vigilant lifeguards one might almost mistake it for a pagan immersion ceremony. And yet this is Hampstead Heath, only four miles from central London.

The idyllic scene reflects the growing popularity of "wild swimming".

Isabel Robinson, a 20 year-old student has cycled all the way from south London to get here. "It's fun, like being on the beach but in a city - a real novelty. The water's quite cold but on a day like today it's refreshing."

James Townsend, a 32-year-old office worker hurriedly pulling on his trunks, says there's no comparison with a swimming pool.

"I don't like chlorinated water or lanes. I come from the middle of nowhere in mid-Wales and to me this feels like the countryside."

After a hard day working as a windfarm developer, this is the moment he looks forward to.

No diving, no bombing? This is no rules swimming

"As soon as you dive in and feel the water go down the back of your neck, you relax. It's fantastic."

Wild swimming is the name the publishing industry invented in 2008 to kickstart a new literary phenomenon. Two books with almost identical names - Wild Swimming by Daniel Start, Wild Swim by Kate Rew - were published, detailing hundreds of waterholes across Britain.

The term's meaning is not always clear. For some it's simply swimming in rivers and lakes, others include beaches, while some add in lidos - large outdoor pools.

You might throw London's River Thames into the mix, after Times columnist Matthew Parris indulged in a spot of wild swimming on this famous waterway. The former MP wrote about his troubled swim across the Thames - he got swept three-quarters of a mile upstream - in Saturday's edition of the Times. The Port of London Authority fiercely condemned Mr Parris' actions, claiming he could have caused a boat to swerve, risking collision with "another vessel or bridge or pier".

But most wild swimming is done in less high profile places.

Surfing echo

People have always swum outside but as more and more indoor pools were constructed in the post-war period, it became a rather eccentric habit. But in the last few years a dramatic resurgence has taken place, Ms Rew argues. Membership of the Outdoor Swimming Society, founded by Ms Rew, has doubled every year since its formation in 2006 and mentions pop up in the strangest places - this year's International Conference on the modernist writer Virginia Woolf, even included a paper on wild swimming.

"I think we've reached a tipping point where outdoor swimming is becoming normal again," Ms Rew says. "There's always been a hardcore of people who never stopped swimming outdoors. But until now they were an ageing group."

In an echo of how surfers behave, a new generation is using social networking sites to plan swims, she argues.

"My enlightenment moment came a few years ago when I planned to go up to the Lakes to swim. Prior to that it had been an opportunistic thing. It's a bit like with surfers - you don't visit somewhere to go to a restaurant or cultural place, you're going there to swim."

So what is it about wild swimming that inspires people to keep diving in?

"There's very little joy to be had in a public swimming pool," she says. "But there's a slightly inexplicable magic to swimming outdoors. As soon as you jump in it feels like the best thing ever - it's the change in physical state. You're floating and get a completely different perspective of the landscape and wildlife. You notice tree roots, swim up to water lilies and see dragonflies mating."

Indeed, in a survey of OSS members, 83% said they swam outdoors because it made them happier and less stressed.

Sandra Moran is an accountant by day but after work swims with friends in Lincolnshire's River Witham.

Frog's eye view

"I used to swim in the North Sea but now river swimming is my favourite. The water's so soft. It's the frog's eye view that [the late writer and environmentalist] Roger Deakin wrote about - you can hear the midges, see the pollen landing on the water and feel the current pushing gently against you."

The rise of river swimming is due in large part to environmental improvements in the last couple of decades, she says.

"When I was young there was crop spraying from light aircraft and the rivers were yellow and thick with chemicals. The farming's less intensive now, there' much more wildlife. Where we swim it's really clear and more than 20 feet deep."

Harry Eyres who swims at Hampstead ponds and writes the Slow Lane column for the Financial Times, agrees that the late Roger Deakin was a crucial pioneer. For his 1999 book Waterlog, Deakin travelled around Britain, swimming his way through streams, lakes, lidos and coves, turning each dip into a meditation on nature and modern man.

"Waterlog was really seminal," Eyres says. "There's always been oddbods enjoying outdoor swimming. But no-one had turned it into a philosophy before. And Roger was a very eloquent guy, quite dashing with an outlaw spirit."

And while most wild swimming doesn't trouble the authorities, that outlaw spirit - some would call it recklessness - is apparent in some outdoor swimmers' psyche.

Legal grounds

The legality of swimming in inland water is "complex and unclear", says Nathan Willmott, a partner with law firm Berwin Leighton Paisner, who advises the Outdoor Swimming Society.

Is wild swimming safe?

• The Royal Society for the Prevention of Accidents says in 2006, 21 deaths were due to swimming in inland water
• The Port of London Authority says it has rescued 14 swimmers from the Thames in the past six months, and there has been one fatality
• Supporters of wild swimming say it is safe as long as one follows some commonsense rules
• Its advice includes always swimming with somebody else, being sober and thinking about currents, tides and where you're going to get out

There are no set rules for different bodies of water such as rivers, reservoirs or ponds, and each section of water must be weighed up against a number of criteria.  According to ancient case law, one can only swim in "navigable waterways", a test that relates to the passage of boats rather than swimmers.

"There isn't really a book to look in to see if a particular section is navigable, whereas with walking you can look on an Ordnance Survey map for rights of way," Mr Willmott says. 

Then there may be local bylaws forbidding swimming, which will cover particular stretches of water, although tracking down any applicable ones is a difficult process in itself, he says.  There is also the question of land ownership, which may prevent swimmers from getting to the water. 

Last month, British Waterways, which manages Britain's historic canals and rivers, advised against taking a dip in its waters, suggesting swimmers "choose somewhere suitable, such as a swimming pool or lido" instead.

As for Matthew Parris's Thames dip, Mr Willmott says a solicitor would currently be hard pressed to say whether such a swim was legal or not. But London's chief harbour master, David Snelson, calls it "ignorant and selfish".

"Basically, swimming in the Thames is equivalent to taking a walk down the M25."

Below is a selection of your comments.

I am 30 and growing up in Canada I hardly ever swam in pools. Instead I preferred lakes, ponds, streams and rivers. Of course there are dangers, but I was taught to be wary of unfamiliar water and to avoid currents. I think it is sad that swimming in natural bodies of water seems to be a novelty, but I am glad that people are rediscovering it!

R. Passmore, Ottawa, Canada

Having relocated to India some 10 months ago, the opportunities to go Wild Swimming are massive - and with some absolutely spectacular scenery to boot. However, having spent three hours in a river last weekend I wasn't too happy when i saw the 6ft crocodile on the riverbank on my way out. I don't think I'll be Wild Swimming out here again any time soon.

James, Bangalore, India

Swimming in inland water is perfectly legal across Scotland under the terms of the Land Reform (Scotland) Act 2003. The claim from Nathan Willmott only relates to England and Wales.

Andy Wightman, Edinburgh, Scotland

I and a friend swim in a stretch of the Thames at least twice a week, a mile up steam and a mile downstream. Not advisable for the novice swimmer, but we take sensible precautions such as a brightly coloured swim hats and someone on the bank if we're heading out for a longer swim. I take the same precautions as I might do walking along a busy stretch of road, and I accept all the risks that come with it. It's safer than binge drinking on a Saturday evening in central Oxford!

Kelvin Fowler, Oxford

I grew up swimming in lakes, but I would never swim in the Thames any more than I would the Mississippi or Hudson. These rivers are swift, dirty, and full of boat traffic. Lots of Americans grow up either living by or vacationing on lakes, but since it's part of childhood, we are intimately familiar with safety issues. We never swim alone, we always know what the lakebed is like (depth, sandy or rocky, where the drops, sandbars, and drowned trees are), and weak swimmers stay close to the shore. Boats are separated from swimmers with "No Wake" buoys.

Renee, New York, NY

On a recent trip to my hometown of Abergavenny a casual walk along the river Usk turned into a most relaxing, rejuvenating and enjoyable swim. There were signs in some areas indicating swimming was not allowed, but this was rightly being ignored by a number of happy, refreshed swimmers. But swimming in a river crisscrossed by boats is lunacy!

Alan, Falmouth, UK

I remember in the late '40s there was a lot of swimming at Virginia Water, including by my mother, and in the Thames at Runnymede. But there were deaths too - from cramp through going into cold water soon after a meal and from currents in the river. I wouldn't want to do this ever (even if I could swim) but I find the idea that it is illegal, offensive. There were humans in these islands swimming in rivers and lakes before there were boats or land ownership so they have the rights of prior use.

Peter Smith, Bridgend, South Wales

Seriously? This is some kind of revolutionary phenomenon? I suspect this new "wave" of swimmers are urbanite adults who stumbled out of the city one day and were amazed to find a load of wet stuff lying around that they can float about in. Those tall green things, we call those trees. The small fluffy white things are sheep. Any more questions?

Ric Hardacre, Ipswich, UK

A friend of mine lost his 18 year old son, "wild swimming" in a lake. He was a strong swimmer too but went under before his mates could get to him. The article makes no mention of the damaging and potentially fatal Weil's Disease (leptospirosis) either. Matthew Parris's stunt was just stupid. Apart from the fiercely strong tides and current there's a lot of traffic in that part of the Thames including some quite large ships and fast pleasure craft many of which don't keep an adequate look out and who could easily miss a swimmer if they did.

Phil, Oxford, UK

Like any other sport, if you approach open water swimming with a level of respect and caution it is perfectly safe. There are many venues around London that provide a safe environment for open water swimming. The pools in the UK are sub-standard and inadequate for long distance swimming training.

Bec, London

While wild swimming in rivers and other stretches of water may be safe in some places, it's important to remember that many of Scotland's lochs are very, very cold. Almost every summer people drown because they have underestimated the cold, even in the hottest weather. Going any distance from the banks is a risky business unless you're properly prepared.

Sandra, Fife, Scotland

I was 11 years old in 1970 and swimming in local rivers and lakes around County Durham was normal, especially on a hot summer's day. It just shows how 40 years of paranoia, council scare mongering and intrusive Health and Safety nonsense has been ingrained into peoples' consciousness.

Gary, Wisbech, UK

Oh dear. Here we go again. People rediscover an ancient and innocent pleasure such as swimming in natural water ... and onto the stage jump lawyers, know-alls, the health-and-safety-brigade and any other challenged person who thinks they have an opinion worth hearing. What is wrong with this country? In none of the continental countries I have visited, worked in or lived in is this even remotely an issue.

Chris, Cardiff

I regularly swim in the Thames near Wallingford. The water quality is high (check on the Environment Agency website for your area) and there is very little boat traffic. The risk of Weils disease is minimal actually in the water according to my doctor. You would really need to be eating wet mud from a section of riverbank used regularly by rats. Having said that, basic commonsense says to not drink the water!

Tim, Oxford, UK

I certainly would swim in a body of water, wherever it may be, except the Thames. Nothing to do with the water quality, or danger from waterborne craft. More to do with the idea that Mathew Parris might be lurking there, in the shadows, in his Speedos and that namby pamby grin.......waiting!

Paul Dahne, Swansea