No chlorine, no roof and definitely no heating: Roger Deakin dips into his personal, and wet, odyssey across Britain - and discovers the lengths some other swimmers will go to. Photographs by Jason Lowe
Once upon a time most people swam in the open air. But in the past two or three decades, the tables have turned, and the outdoor swimmer, especially the wild variety, is now an endangered species. Yet, as I discovered during the course of my recent swimming journey through Britain, there are pockets of resistance everywhere, and as we return towards all things natural, "wild swimming" may be poised for a renaissance.

The notion of a swimming journey had been inspired by John Cheever's classic short story "The Swimmer" (made into a film starring Burt Lancaster), in which the hero, Ned Merrill, decides to swim the eight miles home from a poolside party on Long Island via his neighbours' swimming pools. I have always found swimming a great liberator of the mind, a kind of meditation, so to travel amphibiously, joining up the pale blue lines and inkspots on the map, seemed to offer an opportunity to learn about our land from a new perspective. The swimmer and the writer in me both shared a single aim: to leave our baggage behind on the bank, the beach or the poolside and float free.

There is a distinct divide among swimmers, between those who favour pools and the free spirits like myself who abandon themselves to the sea, or bathe in secret swimming holes in rivers, lakes, ponds, lochs, flooded quarries or tarns. Even the pool swimmers subdivide into two great clans: indoor and out. Iris Murdoch famously called swimming pools "machines for swimming in", and always bathed in rivers or the sea - few swimmers enjoy chlorine after the sweetness of natural water. Some of the open pools, however, especially the lidos of the Twenties and Thirties, have an architectural beauty and atmosphere of their own. Most of them have gone, or are going, like the magnificent Tinside Lido at Plymouth. Others have been snatched at the last moment from destruction, like the tidal Jubilee Pool at Penzance or RWH Jones's streamlined, elegant Saltdean Lido near Brighton.

The architecture of wild swimming, in so far as it exists, tends more towards the homespun. The classic sign of a secret swimming hole is a knotted rope dangling from an overhanging branch and perhaps a makeshift plank diving board, a submerged ladder by the bank, or a jetty.

On the banks of the River Frome at Farleigh Hungerford, near Trowbridge, there is a swimming club whose newsletter is full of evidence of the wild swimmer's eye for detail: "The lower of the three-tier diving boards, which was a little wobbly last year, has been fixed. The downstream bank ladder was replaced at the end of last year, as the previous one had most of the lower rungs missing."

The club is almost 70 years old and has as many as 2,000 members. They bathe from a riverside field, by courtesy of the farmer, Phil Bryant, and their south-facing grassy hillside swoops down to a water meadow, and the river. They have a wooden changing hut, whose tin roof warms it up nicely on sunny days. The fine set of three-tier diving boards, originally made by George Applegate, a local engineer, has just had to be dismantled because the health and safety people came and plumbed the lovely river pool, which generations of swimmers had thought fathomless, and found it several centimetres less than the new regulation depth. I had dived in myself and lived to tell the tale. So had others, for nearly 70 years. But you have to move with the times.

Rob Fryer, the club chairman, enjoys the sense of tradition and camaraderie between the generations of bathers who have enjoyed "Real Swimming", as they call it at the club. Almost everyone in Trowbridge has come out to swim here at some time in their life. Leonard Applegate, now 77, remembers riding his new Raleigh bike down to the club for a swim in 1935. "The banks were filled with

people, hundreds of them, picnicking and swimming," he says. "We would often come down for a dip at six o'clock at night after work." He still visits the river from time to time, although he was off to swim in Lanzarote this week.

Not far away, in the leafy outskirts of Bristol, is the Henleaze Swimming Club, a beautiful flooded quarry, fed by springs, that has been a swimming club since the Twenties. You walk down a genteel suburban avenue and through the club's elegant ironwork gateway into another era. The lake winks beyond the weeping willows and lawns. This unexpected canyon, surrounded by allotments and back gardens, is only three miles from the city centre. No wonder it is popular, and even, in its quiet way, exclusive. Membership is limited to 1,300, and the waiting list usually hovers around 800.

Unusually, these days, the club boasts a fine set of high diving boards. Only the topmost 10-metre board is reckoned too high by modern standards and has had to be removed, leaving boards at seven and five metres and a tempting two- metre springboard. "People went off that top board for 50 years without any problems," one member told me. Olympic divers used to visit the club in the Thirties and Forties to give displays.

The Henleaze quarry was originally flooded in 1912, when workmen struck the springs that still supply the clear, sweet-smelling water. It was bought by a doctor, who allowed a group of Bristol swimmers to form the Henleaze Club in 1919. Men changed behind a canvas screen, women in a marquee. It was only later, when they had bought the lake for pounds 450 in 1933, that the club built its elegant women's pavilion. The men have their own sunny enclosure tucked away on another bank. They have two regulars in their eighties, and on the opening day of the season, 24 April, one 87-year-old swimmer always makes a point of arriving a quarter of an hour early in order to be first in. This year it was 50 degrees Fahrenheit, and the youngest swimmer was eight. The season here usually lasts until the end of September.

One regular at the Henleaze quarry pool, Carol Freeman, regards it as a blissful sanctuary: "There are few places in cities where you can find peace like this. You're in the middle of Bristol, but it's so calm you could be anywhere on earth. Even on a hot day, with 300 people on the lawn, you can swim far out, and the world drifts away."

At Brighton, the oldest continuously running sea-swimming club still meets every morning at one of the arches under the promenade near the Palace Pier. The Brighton Swimming Club was founded by local sea swimmers in 1860, but today there is only a nucleus of 20 salt-water aficionados left in a club that has 500 members, most of whom opt for the predictable comforts of the indoor pool.

The sea bathers go out in all weather, throughout the year, and their Christmas Day swim is a local tradition. John Ottaway, their chairman, told me the sea had "warmed up to 53 degrees" from its winter level this year of around 40 degrees. Two years ago it went down to 34 degrees at the very moment he had planned his 50th birthday swim. He had no option but to go in. Their senior sea swimmer is Jim Wilde, at 85. Another, David Sawyer, now suffers from arthritis and has to use fins, but can still swim from the Marina to the Palace Pier and back, a distance of three or four miles. He sometimes fishes as he swims, carrying a bamboo cane with a line and tackle and putting his catch - usually mackerel - into a bag around his neck.

Along the coast in Plymouth, another of the great capitals of sea and open-air swimming, the noble art is now almost extinct. The Tinside Lido stands neglected on the seafront awaiting execution by whoever buys the site from the City Council for development. The City has no less than three swimming clubs with over a thousand members between them, and a tradition of sea swimming you might expect in a great naval city. Kevin Richards may be the last great sea swimmer Plymouth will ever see. He holds the record for the annual Breakwater Race and won the last race in 1987. The competitors were taken out by pilot boat to the big stone breakwater offshore for the start, walked along it to the lighthouse, greased themselves in Vaseline and Elliman's Embrocation, and swam for the foreshore at the Hoe, two miles away. Kevin also wore two pairs of trunks against the cold. His record of 38 minutes 53 seconds, set when he was 15, seems likely to stand. And he still has the trophy. Before official alarm about the levels of pollution put a stop to it all in 1991, there were dozens of other regular Plymouth sea swims: a relay race from the Breakwater between the city's rival clubs, a half-mile sprint to the Mallard Beacon buoy and back and even a six-mile swim out to the Breakwater from Saltash Bridge. But the most impressive Plymouth swim belongs to Sharon Price who once covered the 14 miles by sea from Eddystone Lighthouse to the Hoe. Outdoor swimming in London is now limited to a half-dozen places, and they do not include the Thames, where a Port of London authority bylaw forbids bathing. Right in the centre of Covent Garden the aptly named Oasis has an outdoor heated pool that steams gently in frosty weather and is always popular. For natural-water purists, there is still the Serpentine Lido, and up on Hampstead Heath, the three Highgate swimming ponds are one of the glories of the capital. The Women's Pond, the Men's Pond, and the Mixed Pond are to be found, in descending order, down the slopes of Highgate Hill. And they're free. The latter two are delightful, and as far as I can gather, so is the first, the approaches to which positively bristle with notices proclaiming "Females Only". I am told the Women's Pond has some impressively fit 80-year-old swimmers, one of whom injured herself recently vaulting over the railings after hours. The Men's Pond positively glows with health, and there has been swimming here for over 90 years. The busiest time is early in the morning. It is a kind of unofficial club which anyone can join; the very opposite of the smart RAC Clubhouse Pool in Pall Mall. Nudity is much in evidence in the enclosure, where people play chess, read the papers, or do press-ups, but you must wear your bathing suit when you go out on stage into the pond. There are two jetties and a springboard, and the water is so deep that once, during the Thirties, there was a 10-metre board, and the Highgate Diving Club would perform swallow dives before a crowd of 10,000 at the Aquatic Carnival. Terry and Les, the supervisors, have a photograph of themselves on their office wall standing on the frozen pond while swimmers frolic in an ice-hole they have thoughtfully provided. Across the river, Tooting Bec Lido is by far the biggest such pool, and the South London Swimming Club, which runs the pool all winter, dates back to 1906 and has 500 members. The 200 women who swim there are known as the Bec Mermaids, and the south Londoners always race on Christmas and New Year's Day, even if they have to break the ice. The outdoor swimmers' dedication to this place, and the passionate determination that gets 50 of them a day into the icy water all winter, and up to 6,000 in summer, has kept this lido open, and won them the Lottery funds they need to repair and improve the place. If Tooting Bec is a model for the future of outdoor swimming in Britain, wild swimmers everywhere can feel buoyant

`Waterlog, A Swimmer's Journey Through Britain' by Roger Deakin is published by Chatto & Windus, pounds 15.99