Outdoor swimming: come on in, these waters are lovely

High up on Exmoor, beneath the Iron Age hill fort of Cow Castle, lush with its summer coat of vivid green bracken, the River Barle calls. The water deepens as it turns, providing an inviting pool on this hot, sticky summer's evening.

Where wilder in the world than the lake at Wastwater

Despite the heat, the river is freezing and I can't help but gasp as I edge my way in. "Just dive under, Dad," calls my nine-year-old son, smug in his wet suit. I follow his advice and after the initial shock comes the rapture.

The clear water is soft and limpid. I have a flashback to childhood; a return to sea-swimming and stoic plunges into the icy llyns of Snowdonia. I flip onto my back and The Wind in the Willows floats into my memory - the Piper at the Gates of Dawn. The heady sense of freedom and innocence is beguiling; I am at one with the river.

Two turquoise dragonflies shimmy past at eye level. Shoals of tiny trout investigate my toes. I'm aeons away from the treadmill of the roped-off lane in the local swimming pool, laden with chlorine.

This is the world of outdoor swimming, where rivers, lakes, ponds, coves and even lidos are being rediscovered and celebrated.

Wild, or outdoor, swimming is quite simply the thing to do this summer. It chimes perfectly with our craving for a simpler, more honest way of life. It's free (or cheap) and fun. It's also deliciously uninhibited: there's something about the silkiness of natural water that almost demands that you strip off your clothes and slide in for a spot of discreet skinny-dipping, however strait-laced your everyday persona.

It is cousin to organic food, nephew to slow living and brother to our collective yearning for the wild, which was so well articulated by Robert Macfarlane in The Wild Places.

Until the rise of the local swimming pool, Britons lived the life aquatic wherever they found a bit of water. Many towns boasted open-air pools or lidos, while every country child knew the best local coves and river plunge pools, and would leap into slow-moving rivers or splash around in reed-fringed meres and ponds. But those tranquil days ebbed away as indoor pools were built and the authorities warned that it was far too risky to swim unsupervised in dirty, "dangerous", open-air water.

Now, however, our rivers are cleaner and we are sick of being nannied. There's a veritable riptide of people rushing to the water, spurred on by a wave of books on outdoor swimming. First there was Roger Deakin's endearingly eccentric Waterlog: A Swimmer's Journey Through Britain and the seminal Haunts of the Black Masseur: The Swimmer as Hero by Charles Sprawson. Then, this year, came Kate Rew's evocatively photographed Wild Swim and Daniel Start's passionate and practical Wild Swimming.

Aficionado Rob Fryer, chairman of the Farleigh and District River Swimming Club, is exuberant about getting wild and wet. "If you go to a concrete and chlorine pool, you can't take a picnic, the dog and the family, or have boats. Out in the countryside, you're at one with nature and, if you're stressed or tired, there is nothing like jumping into a river on a hot day - you'll feel 20 years younger."

So, without further ado, here is our guide to 50 of the best places to swim outdoors: a gazetteer of watery enlightenment and sensual splendour. This is swimming for pure fun, rather than the drudge of 50 tedious lengths. It's about exploring our countryside through the medium of water.

Do it. You'll love it.