Are Polar Bears—swimmers who brave icy waters from Montana to Moscow— fearless or just plain crazy?Brett Martin plunges into their chilly circle

It's a complicated look, the one that the crowd on the beach was sending my way—equal parts amusement, amazement, pity, and confusion. I know that look well. I used to wear it myself on midwinter days when my father would drive us across Brooklyn to watch the Coney Island Polar Bear Club USA in action. To me, the sight of half-naked men diving into the icy Atlantic was just another carnival attraction like the Cyclone and the Skee-Ball parlors on the other side of the boardwalk. Like sex, cigars, and several other of the more bizarre aspects of adult life, it was certainly nothing I had any intention of ever trying. I was then and still am a cold-water coward, fully capable, no matter what the weather, of standing paralyzed on a diving board for minutes on end, hating the thought of flinging myself over the edge. So I suppose it was ironically inevitable that—drawn by the twin desires of overcoming my fear and becoming a part of a long and distinguished Brooklyn tradition—I would someday be standing on the very same beach in December, dressed only in old sneakers and a bathing suit, about to dive into the water while sensible beachcombers in down jackets gave me the look that said, "Oh, you poor, poor lunatic."

The Coney Island Polar Bears have a pedigree that goes back much farther than my childhood trips to the beach. It was founded by a fascinating and largely forgotten turn-of-the-20th-century figure named Bernarr Macfadden. Known as the Father of Physical Culture decades before Jack La Lanne was even a glimmer in some dumbbell's eye, Macfadden was a fitness guru, millionaire publisher, and master of PR. Between 1899 and his death in 1955, he staged some of America's first bodybuilding competitions; built a publishing empire with titles such as True Story, True Detective, and the sensationalistic New York Evening Graphic; hobnobbed with the likes of FDR and Will Rogers; and founded both a town (Physical Culture City, devoted to outdoor exercise and healthful diet; it's now part of Spotswood, New Jersey) and a defunct whole-grain-based religion called Cosmotarianism. Macfadden was also the author of such tomes as Health, Beauty and Sexuality, The Miracle of Milk, Predetermine Your Baby's Sex, and Muscular Power and Beauty. Among his many tenets for healthy living was the notion that cold water increases one's virility, stamina, and immunity. He was rumored to have founded the Coney Island Polar Bear Club in 1903.

Macfadden wasn't alone in his belief. Faith in the salutary effects of cold water seems to transcend all cultural and geographic divides. The Coney Island Polar Bears have been joined over the years by groups from Vancouver to Moscow—just a small international sampling includes the Ice Bears of Melbu, Norway; Belgium's Royal Swimming Club "De Ijsberen Boom"; the Walrus Club of Hel, Poland (whose members must be familiar with what really happens when Hel freezes over); the people who host the annual Polar Bear Swimming Competition in Pusan, South Korea; and the Panama Swimming Club, which meets not in Panama but in England, on the shores of the frosty North Sea. Stateside, the list includes clubs in Boulder, Colorado; Libby, Montana; Sheboygan, Wisconsin; and, somewhat less impressively, Venice Beach, California. Acting, perhaps, on the belief that you should start the new year as uncomfortably as possible, New Year's Day events punctuate the calendar of many of these clubs (indeed, one could easily make a yearly ritual out of freezing one's tootsies off in a new place every January 1).

In addition to organizing public swims throughout the winter, the network of clubs helps Polar Bears who find themselves far from home and in need of a bracing dip. "I took a trip to Russia a few years ago," recalls veteran Brooklyn winter bather John Sineno. "I met the Walrus Club and we drilled a hole in the Neva River to swim." Until a recent injury sidelined him, Sineno swam at Coney Island every day for decades, as a member of a Polar Bear splinter group called the Ice Berg Athletic Club. He was bullish about the effects I could expect from my own date with the cold, cold sea. "If you do this every week or so, it will make you feel sharper, more alert, and younger," he said. "It will help your sex life, too. I'm sixty-eight, and I'm not a Viagra guy."

I tried to keep that in mind as I approached the boardwalk. By sheer coincidence, it was about 50 degrees and sunny out—hardly the worst that a New York winter has to offer. This was both good and bad: I had slightly less chance of freezing to death upon exiting the water—then again, the surf temperature was still hovering around 36 degrees. This meant that I'd be swimming in near-freezing water but none of my friends would give me credit for it because of the unseasonably warm weather.

"You won't be able to miss us," club treasurer Tom McGann had told me. He wasn't wrong. Mild weather notwithstanding, there still weren't many people wearing bathing suits. In my memory, the Polar Bear Club was made up of older men with thick Eastern European accents and thicker potbellies. But the 20 or so members who had gathered on this Sunday were one of the most diverse groups I'd ever encountered, even in New York. Among them was a man who traveled from Connecticut each Sunday, two Japanese sushi chefs, an intimidating 71-year-old named Yuriy who'd cut his teeth swimming in a Moscow park and was killing time by doing pushups, and Montserrat, an excited 40-year-old woman from Ecuador. Montserrat told me she had started participating in the swims after September 11, 2001. An organizer of banking events, she had worked across the street from the World Trade Center, and her experiences that day instilled in her a desire to test her limits. "You never know how much time you have left," she said.

When everyone had arrived, we headed down to the beach. The truly hard core left their towels behind, though I was assured that bringing mine would be no mark of shame. We formed a circle at the water's edge. With the gusto of a Marine drill sergeant, longtime member Mike Spataro delivered a chant to get us psyched up. It began "I don't know but I've been told / Coney's water's pretty cold." I don't remember the rest, because by the second verse—without any pause to let us chicken out or worry about heart attack or hypothermia—we were dashing into the waves and all the blood was rushing from my head.

Now, I had been in cold water in the past, but nothing had prepared me for this. My legs immediately disappeared beneath me, replaced by numb, leaden stumps. We again joined hands and danced around in a circle, shrieking "Polar Bears! Polar Bears! Polar Bears!" My insides felt as if they were trying to leap free of my body, but every inch of my skin was tinglingly alive. The circle broke up as we each celebrated in our own way. Montserrat jumped up and down, screaming joyfully and throwing handfuls of water in the air. I dunked my head under and came up screaming myself. Yuriy sat placidly, submerged up to his neck, hardly moving.

After a few minutes, my legs began to cramp and throb painfully. Strangely, I found I was reluctant to leave the water, not only because I wanted to somehow savor the fleeting, excruciating moment, but also because, in that short time, I had forged a connection with my newfound friends—the kind of bond that comes only by living through something intensely stupid.

I eventually waded out of the surf. The air was warm on my bright red skin; I felt as if I were sparkling. Once again, I could see the bemused, pitying expressions on the faces of onlookers. Only this time, I thought I also saw something else. I may have been crazy, but I could have sworn it was envy.

BRETT MARTIN has written for The New Yorker, GQ, Esquire, and Details. He lives in Brooklyn, far from the water.