n 1973, Roger Deakin, a British writer and environmental activist, acquired a tumbledown sixteenth-century farmhouse outside the ancient village of Mellis, in Suffolk, and began a restoration, repairing stone walls and replacing roof tiles. Among the attributes of Walnut Tree Farm, as the house was called, was a deep, spring-fed moat. It didn’t surround the house, as with a fortified castle, but was excavated into the land, in roughly parallel lines, at the front and the back of the property. The moat had served its original, Elizabethan owner as a water supply, a cooler, and a status symbol. Over the centuries, it fell into disrepair, becoming silted up from falling leaves and rotting tree roots. Deakin had the moat dredged to a depth of ten feet; staked a wooden ladder by the bank, near the spreading roots of a willow tree; and began regularly swimming in the cold, greenish water. He gained what he called a frog’s-eye view of the changing seasons, and an intimate familiarity with the creatures sharing the moat, from dragonflies to newts.

In the mid-nineties, Deakin took inspiration from the protagonist of John Cheever’s short story “The Swimmer”—who traverses his suburban neighborhood pool by pool—and made an aquatic journey around England, Wales, and Scotland, bathing in seas, rivers, ponds, and lakes. Deakin wrote a book about that adventure, “Waterlog” (1999), which has become a classic of British nature writing. His prose is sensuous—“At seaweedy Kimmeridge I mingled with mullet too lazy to move”—and his sense of humor is as dry as his theme is wet. A leech, he observes, keeps changing shape in the water, “looping and stretching out its black stocking of a body, as women do when they’re testing tights for quality in Marks & Spencer.” The book also displays a lively erudition: when Deakin describes a swim off the virtually unpopulated island of Jura, in the Scottish Hebrides, he notes that George Orwell retreated there to write “1984.”

“Waterlog” is subtly political. Deakin was intent on challenging the privatization of once public waters. “The right to walk freely along river banks or to bathe in rivers, should no more be bought and sold than the right to walk up mountains or to swim in the sea from our beaches,” he writes. In one rousing passage, he yells back at censorious river keepers who chastise him for swimming in the trout-filled Itchen, which runs through the grounds of an élite boarding school: “I already felt invigorated after a really first class swim, and now I felt even better after a terrific set-to.” For Deakin, swimming in open waters is a subversive act—a way to reclaim nature cordoned off by capitalism, and to “regain a sense of what is old and wild in these islands.”

Deakin died, from a brain tumor, in 2006. A year later, Walnut Tree Farm was bought by a couple, Jasmin and Titus Rowlandson, who have maintained his commitment to ungentrified country living. There is still no central heating in the farmhouse; it is warmed by an Aga stove and an enormous open hearth, over which dinner is typically cooked. Last year, Titus, who restores classic automobiles in the barn, and Jasmin, a jeweller and a painter, began offering overnight stays in two renovated cabins on the property. In early November, I took the train from London to Suffolk, with the aim of swimming in Deakin’s moat. Heavy rain had fallen all morning, sluicing the windows of the train as it rolled through the port of Ipswich. Deakin’s book begins with an ecstatic moat swim in summer rain, amid “water sprites springing up on tiptoe like bright pins over the surface.” A chilly, wet autumn day seemed considerably less enchanting.

By the time I reached Walnut Tree Farm, however, the rain had stopped, and low streaks of pinkish afternoon sun had emerged between torn clouds and the bare branches of sodden trees. After installing myself in the cabin I’d rented—delightfully kitted out with antique furniture, a wood-burning stove, and a well-chosen library—I put on my bathing suit, along with neoprene booties and gloves. Straightening my spine, I headed for the back-yard moat. Sixty feet in length, it had a gleaming black surface strewn with the golden disks of fallen leaves, like tarnished Anglo-Saxon jewelry inlaid with gems.

Descending the rickety ladder, I pushed off into the water and breaststroked to the deepest part, at the center, to avoid entanglement with hidden weeds and roots. The cold was searing. I could feel the muscles of my upper back constricting; my clavicle and upper ribs seemed ready to shatter, and my toes and fingers started to numb, despite my high-tech gear. I swam a few lengths, trying to appreciate Deakin’s frog’s-eye view, though, to the extent that I could identify with a frog, it was with one placed—in the reverse of the fable—in a slowly chilling pot of water, to see if it notices when it starts to freeze to death.

The lifecycle of garbage.
Cartoon by Roz Chast
Despite the cold—and despite the two hours it took me to warm up afterward, stoking the wood-burning stove and drinking as much tea as I could handle—my brief swim in the moat was a starkly beautiful experience. I felt fantastic. Deakin swam in the moat nearly every day, except when it froze over, and it was easy to see how he’d got hooked.

I was not the only reader of Deakin to have been seduced in this way. “Waterlog” helped spur the rise of what has become known in Britain as “wild swimming”: wading briefly or churning doggedly in outdoor waters, rather than doing laps in indoor pools. According to the most recent figures collected by Sport England, a group that urges physical activity, half a million people in England are engaging regularly in wild swimming—nearly twice as many as reported doing so just three years ago. Many participants claim that the activity is not only fun but also improves their mental health.

The sport’s attractions can be hard to imagine if your vision of outdoor swimming revolves around sunshine, warm water, fine-grained sand, and a trashy novel to read afterward. Britain has an abundance of “blue space”—a term used to characterize rivers, ponds, lakes, and seas by people who argue for the health benefits of having access to them. There are about forty thousand lakes in Britain, and it’s estimated that nobody in the U.K. is ever more than seventy miles from a stretch of coastline. But British waters are incontrovertibly cold. Sea temperatures rarely creep above twenty degrees Celsius, or sixty-eight degrees Fahrenheit, and England’s freshwater bodies, which are often fed by underground springs, tend to be even chillier. Last year, by mid-October—generally regarded as the end of the outdoor-swimming season—the Serpentine Lido, the designated swimming spot in the Serpentine lake, in London’s Hyde Park, had dropped to the low fifties. The hardiest wild swimmers keep going even when water temperatures fall below freezing; they pack, along with a microfibre towel and a thermos of tea, an axe, for breaking a channel through the ice.

The vogue for outdoor swimming has been fuelled, in part, by the Internet. It’s easy to collect “likes” by posting a photograph of yourself waist-deep in a craggy loch. The British press provides travel advice about the most romantic swimming locales. The Guardian recently gushed about a spot at the foot of Mt. Snowdon, in Wales, noting, “Take a dip here and you are swimming with the Torgoch, a rare type of Arctic char fish that has survived since the ice age.”