Splash mob: The British have enjoyed a long love affair with wild-water swimming

Susie Parr reveals the true appeal of an icy dip

Sometimes, on a windswept beach, as – in time-honoured, British fashion – I am wriggling into my costume under a flapping towel, I wonder what compels me to swim. If I come across an alluring stretch of river, lake or sea, and if conditions are right, I simply cannot resist getting in, even on winter days when the water is shockingly cold. What makes me do this? The bemused glances of passers-by, together with the fact that I am usually the only one in the water, can make me feel embarrassed and furtive. I wonder if I really am behaving as oddly as people seem to think. But swimming outdoors, in cold open water, feels fundamental to me, as if it's in my blood. I learnt to swim in the peaty pools of the River Esk, on family holidays in the Lake District. My mother, despite being myopic and profoundly un-sporty, loved to swim in the River Tay at Broughty Ferry near Dundee. My Swedish grandmother bathed in Lake Siljan, in Dalarna, during the long, light summer days of her youth.

But I am a lightweight compared with the stalwarts, many in their seventies and eighties, who swim every day of the year at Brighton, Hampstead ponds, St Peter's Port, Clevedon and Cambridge. For numerous individuals and groups across the UK, a dip is an unmissable part of the daily routine, even when snow settles on the beach or river bank and the air is icy.

I wanted to find out what lies behind this tradition of cold water swimming. I had assumed that bathing in Britain started when the Victorians discovered the seaside, but as I began to read and research I found a long and fascinating history stretching back through the centuries. Swimming and bathing feature in British art, literature, music and educational treatises from the earliest days. It appears in accounts of the Roman invasion of Britain and takes on a supernatural aspect in Anglo Saxon poetry. The Nordic kings and earls of Orkney were famed for their heroic swimming feats and competitions. Welsh mercenaries, brought to Shetland by their Viking employers, took to the waves in a cleansing ritual that they hoped would win them the favours of local women.

Sir Everard Digby took an esoteric approach to the practice when he wrote De Arte Natandi, a manual in Latin for would-be swimmers of good birth. Illustrated with woodcuts, the book was translated into English and rendered more down-to-earth by Christopher Middleton in 1595. Swimming was seen as a worthy skill for young gentlemen to acquire and Middleton's Art of Swimming deals with the same sorts of practical issues that today's wild swimmers also have to consider: checking the depth, watching out for obstructions, making sure one can find an exit point. Women who bathed were represented in a very different light. Popular ballads, written between 1690 and 1710, suggest that young females who cooled off in rivers or ponds were seen as legitimate sexual prey; swimming assumed an erotic charge.

But then swimming took a rational turn and played a part in the scientific and medical advances of the 18th century. Initially, medicinal sea-bathing – which must have astonished the local residents of British seaside towns and villages when the first bathing machines trundled on to the beach – was only practised by the wealthy and genteel, discerning types who could simultaneously enhance their health and demonstrate their sensibility and appreciation of the picturesque.

For the British Romantic poets, bathing and swimming had a special significance. As a child, Wordsworth bathed in the River Derwent, his immersion symbolising his sense of interfusion with Nature. Shelley was mesmerised by the mystical properties of water and drawn to bathe in it whenever he could, although he never learnt to swim. And Byron was an extreme, dramatic and daring swimmer. His aquatic feats enhanced his celebrity status and he prized his crossing of the Hellespont above any literary achievements.

But the exclusivity of sea bathing was not to last: industrial advances and the advent of rail travel enabled the masses to take to the water. This resulted in class conflicts – with bathing at their heart – being played out on British beaches. The consequent flurry of regulation coincided with the building of municipal swimming pools across the UK. By the end of the 19th century, most decent-sized towns in Britain – even the most landlocked – had a pool and a swimming club. Swimming even took on a political aspect: as women progressed towards suffrage, they started to campaign for mixed bathing, swimming lessons, more functional swimwear and the right to compete. DH Lawrence made an explicit connection between swimming and sexual power in his novel Women in Love, which was published in 1920. The two heroines come across a man swimming naked in a woodland pool. It is Gerald Crich, who will become Gudrun's lover. The sight of his white flesh and thrusting strokes deeply excites Gudrun and awakes in her a profound envy of male freedom. Heady stuff indeed.

The two World Wars put the sea out of bounds and caused many pools to close, so swimming in rivers, lakes and ponds became popular once again. And in a climate of austerity, post-War Britons had to enjoy their summer break on a shoestring in holiday camps and campsites around the coast. But, as the restrictions eased and money started to flow, they began to venture further afield, travelling down through France and into Spain and Italy. The appeal of our windy native beaches, cold, heavily-polluted seas and rivers tainted with industrial and agricultural effluent diminished once we got the chance to paddle in the warm, clear waters of the Med. The advent of affordable jet travel meant that, by the 1970s, Benidorm was starting to eclipse Blackpool as a favourite holiday destination. The number of bathers in our native waters was beginning to dwindle.

At the same time, modern indoor sports centres with heated pools were appearing across the country, even in remote areas. Once-popular lidos and tidal pools – the latter built to allow people to swim safely where the sea was treacherous – fell into neglect and many were eventually closed on health and safety grounds. The process of struggling into one's costume in a chilly wind or relentless drizzle started to lose its appeal once the tepid safety and predictable conditions of the indoor pool became accessible to all.

But foreign holidays and heated water did not completely put a stop to outdoor swimming in Britain. The traditional sea swimming clubs quietly continued with their daily rituals and are now starting to attract newer, younger members. And long-established organisations like Farleigh and District Swimming Club, Henleaze Lake in Bristol and Newnham Riverbank Club in Cambridge have managed to weather periods of declining membership and seem to be entering into a new phase of popularity. There are also encouraging signs of a resilient folk memory of traditional bathing places. A hot summer's afternoon will see young people appear, as if by magic, at river pools where their parents and grandparents swam.

The recent wild swimming phenomenon, inspired in part by the late Roger Deakin's book Waterlog, has also effected a welcome revival of interest and made bathing out of doors in Britain cool and glamorous once more. It may be part of the zeitgeist, but this movement is not entirely modern. It has historical roots in Romanticism and in a tradition of heroic swimming that extends beyond Byron to Beowulf. Today's wild swimmers are political animals, too: many focus on campaigning for increased access to rivers and lakes in the face of opposition from health and safety officers, water authorities, the Environment Agency and landowners who want to protect lucrative fishing rights.

The new wild swimming guides have comprehensively re-mapped Britain; they are atlases not of road networks but of bathing places. While working on a book about the history of swimming, I created my own compendium of special places to swim. But my catalogue of swimming places is determined by history rather than geography. For each phase in the history of the activity I travelled to a different part of the British Isles in order to swim in a way that was in keeping. So, in order to better understand Romantic bathing, I swam in the Lake District, re-visiting the river pools of my childhood. I also took a quick plunge in the dismal Byron's Pool at Grantchester, trying to disregard the alarming notices that forbid bathing and warn of dangerous currents. Thinking about early British swimming, I attempted a swim from a beach on Sanday, Orkney, where I was spooked by the presence of a Finwoman scarecrow in a thick sea fog. And to gain an insight into the democratisation of swimming I visited the recently restored Tunnels Beaches in Ilfracombe – a remarkable feat of Victorian engineering – where crowds of lady and gentlemen swimmers were once kept apart by a bugler stationed on an outcrop of rock, ready to sound the alarm if any impropriety was witnessed.

Taking to the water in Tenby, one of Britain's earliest and most elegant sea-bathing resorts, the swimmer can read the town's history in the walls, buildings and steps that merge into the cliff-scape. Here, a humble fishing harbour, with low-built houses that turned their backs to the elements, was opened up by Georgian entrepreneurs. Fine mansions, with large windows facing out towards the sea, arose on the cliff top so that visitors might fully appreciate the splendour of the ocean vista after their health-giving dip.

Swimming at Tenby, despite the town's exceptionally clean and inviting water, I am usually the only one in. I reflect on my collection of postcards from the early decades of the 20th century that show large groups of workmates, friends and neighbours bathing at Margate, at Westward Ho! and Cleethorpes, huddled together in their hired costumes, grinning back at the camera, having fun in the water. Nowadays, it is rare to see groups of swimmers such as these other than at organised events such as charity swims or triathlons, which tend to be serious and grimly competitive affairs. I seldom see families swimming together. More commonly, wet-suited children play in the shallows with a bare-footed adult keeping watch at the water's edge, arms folded and trousers rolled above the knee.

I often speculate about the many possible reasons for the decline in our outdoor swimming habits. Despite the resilience of the traditional clubs and the enthusiasm generated by the wild swimming movement and the triathlon industry, I fear we are in danger of losing something very deep and long-established in our culture: the simple joy of a dip in river, lake or sea – as Daniel Start puts it: "the feral feel of cold water on skin". And it is not just a matter of endorphins. Immersion in cold water has long been understood to alleviate many ailments, from hypertension to depression (physician Sir John Floyer's History of Cold Bathing, published in 1715, shows how cold water played an important role in folk medicine before sea-bathing became fashionable). David Sawyers, one of the Brighton sea swimmers, is an advocate for the curative properties of a cold sea:

"Arthritis first showed up in my toes, then it caught me in the neck and the spine. I found movement became very painful indeed and I couldn't do what I wanted. I lost myself. And it was literally in the water I managed to find myself again. There is a suggestion that the cold can dampen inflammation and I do have a greater freedom of movement in the water than on the land without irritating damaged joints. That's why – come rain, shine, sleet or snow – I will battle my way down to the beach and get into that water."

I hope that The Story of Swimming will enable swimmers like myself to benefit from taking a historical perspective on their passion. Gazing down into the depths, we might start to understand a bit more about why we swim as we do and, rather than being embarrassed, feel proud that we are continuing to uphold a precious but fragile tradition.

'The Story of Swimming' by Susie Parr is published by Dewi Lewis Media, £25