It was so quiet.

The only sound was the wind, rippling and snapping the prayer flags that ran down the riverbank, freezing the paddlers' hands as they zipped into drysuits. It came from upstream, from flat across the Tibetan Plateau, and it drove dry snowflakes onto the beach and darkened the jade-green water with patterns like woven fabric.

The kayakers moved quickly—pulling on life vests, helmets—and didn't speak. After ten years of planning, there wasn't much to say. They were seven of the best expedition paddlers in the world. Led by Scott Lindgren of Auburn, California, the young men represented the vanguard of river exploration, and they had come to Tibet to attempt the first whitewater descent of the Tsangpo Gorge, arguably the last great adventure prize on earth.

The gorge was a Himalayan chasm so shrouded in mystery and danger that a legendary waterfall in its depths, sought by explorers for more than a hundred years, was never even photographed until late in the 20th century. And it was a place, like Everest, that shimmered with mythic lore and menacing superlatives. By some measures, it is the deepest river gorge in the world—three times deeper, with the river tilted eight times steeper, than the Grand Canyon. Running close to a thousand miles from west to east across Tibet at roughly 10,000 feet above sea level, the Yarlung Tsangpo enters the gorge and loses almost all of its altitude in a thundering 150 miles. Along the way, it carves a deep channel between the great peaks of Namcha Barwa (25,446 feet) and Gyala Pelri (23,462), which stand only 13 miles apart. To Buddhists, the gorge is the site of mystical portals to sacred realms; some ancient texts say it will be the last refuge of Buddhism when the rest of the planet falls apart. In an age diminished by the belief that there are no great explorations left undone, the Tsangpo Gorge has remained a fearsome, inviolate anomaly. Nobody had ever successfully paddled the 44-mile stretch of the Upper Gorge from the town of Pe to Clear Creek (beyond which waterfalls make the gorge impassable). No one had ever traveled the length of the Upper Gorge at river level. It is possible that parts of the gorge had never been seen by a Westerner.

And now, a few miles downriver from Pe, Lindgren and the other paddlers of the Outside Tsangpo Expedition carried their kayaks across a wide beach and set them in the sand at water's edge. Here the river was calm and flat, but that would soon change dramatically; the team knew that they were about to attempt an unheard-of combination of high-volume whitewater and vertiginous steepness. The last expedition to seriously attempt the Tsangpo—an American group led by paddler Wickliffe Walker in 1998—had made it 27 miles when one of the team, seasoned kayaker Doug Gordon, drowned in violent rapids.

If anyone could get it done, it would be these seven. Most of them had kayaked since they were children, and each now paddled close to 200 days a year. Lindgren, 30, is the alpha male of expedition kayaking, an Emmy-winning adventure filmmaker who has spent much of the past decade pulling off fast-and-light first descents of some of the Himalayas' most daunting rivers: the Sutlej, the Thule Bheri, the Upper Karnali. His speciality has been river runs combining maximum remoteness, daunting logistical challenges, and extreme audacity—and he's done much of his paddling while hauling a 20-pound Bolex movie camera. He has an improbable and perfect record for bringing everyone home alive and intact.

For the Tsangpo team, he picked his closest kayaking friends, all veterans of previous Lindgren epics. South African Steve Fisher, 26, is known for his prowess in big, violent water. Mike Abbott, 29, from New Zealand, and his paddling partner, Englishman Allan Ellard, 27, are famed for their wild descents, many in the Himalayas. Dustin Knapp, 24, of Jacksonville, Oregon, is the star of many of Lindgren's extreme paddling films; he has launched off so many hair-raising waterfalls and giant drops that he's stopped counting. Twin brothers Johnnie and Willie Kern, 30, from Stowe, Vermont, have a reputation for fearlessness that has spun off its own catchphrase: "If the Kern brothers won't run it, nobody will."

At water's edge on the Tsangpo, just a few miles before the river begins its plunge, the paddlers snugged down into their tightly padded cockpits like fighter pilots and sealed the openings with their neoprene spray skirts. One by one, they picked up their paddles, shoved off the sand, and glided out on the near-freezing current that divided black-timbered ridges rising above 12,000 feet.