WAY BACK in the 20th century, when I stumbled into Yunnan for the first time, I was drunk on sunshine, free love, and two months of third-class rail travel. Here, pressed against the borders of Myanmar and Tibet, in the land the Chinese call "South of the Clouds," I first saw why topography is destiny. After the chaos and heat of the Chinese lowlands, Yunnan was a cool, verdant escape, its green valleys carved by kinetic waters.

Eighteen years later, I feel once again as if I've entered a Taoist scroll painting. Amid long verticals of cloud-kissed peaks and twisting rivers, our five tiny rafts and 21 puny humans flow in harmony with nature, seeing that rarest of things in China: nothing. Shooting north all afternoon in perfect silence, in canyons without people, villages, or electric lines, we jiggle down through fast, easy wave trains, six of us Americans managing the 16-foot paddle raft with immensely tall, goateed guide Willie Kern chanting instructions from behind. The rest are distributed across bigger rafts while guide Jed Weingarten forges ahead on a cataraft, running safety on rapids. The day begins with one good jolting set of rapids and ends with another, called Baptism.

The sun vanishes from these canyons early, so we beach in midafternoon and set up camp and build a driftwood fire. Among the Americans are four Californians—Davo, Des, Roger, and Owen—who've come along with their friend Joe, a vacationing Mountain Travel Sobek guide, for what may be a last shot at this part of the Yangtze. We've also been joined at the last minute by a brother-sister-cousin trio, Jay, Elissa, and Chad, who were traveling through Kunming, the provincial capital.

Our American guides have been running commercial trips on the Yangtze and the Mekong since 2005. Jim hatched the idea in 2001; his father, conservation advocate Ed Norton, had moved here in 1998 to help set up the Nature Conservancy project. Realizing the area's whitewater potential, Jim called two fellow guides to run exploratory trips down the Yangtze, Mekong, and Salween in 2002: Willie, 34, a Vermont-bred kayaking genius who was on the Outside-sponsored first descent of Tibet's Upper Tsangpo Gorge in 2002, and Jed, 32, a grinning, curly-haired photographer and kayaker who speaks admirable Mandarin. (Outside sponsored a 2003 documentary on their efforts, The Yunnan Great Rivers Expedition, narrated by Jim's brother, actor Edward Norton.)

Rounding out our crew is a fourth guide, 32-year-old Californian Ben Fadeley, and two Tibetan guide trainees in their thirties—barrel-chested Yeshi Dorje and lean Tashi Phuntsok—collectively known as the Tibetan Freedom Unit, or the ToFUs. That's as opposed to the SWaFUs, the most important guests on the trip—three young members of a new ecotourism faculty at Southwest Forestry University, in Kunming: park-systems expert Li Xiaolong, a.k.a. "Dragon"; Chen Hai, a skinny, hyperactive lecturer in green tourism; and adventure-sports guest lecturer Duan Lian, who wants to be called "Mr. Exercise." (Using a handheld electronic translator, Li Xiaolong, a calm and chubby 33-year-old with fluent English, hoots as he shows me that their names actually mean Dragon and Exercise.)

Late that night, sleeping heavily on the sand, I'm awakened by a shouted exchange in Mandarin. The SWaFUs are zipped inside one of the tents, in heated discussion. It isn't until the next morning that we learn what it's about. The Chinese professors are worried that, even though this rafting trip has been run successfully five times since 2005, it is illegal. No one has obtained permission from … well, maybe from the National Sports Bureau in Beijing—they aren't sure.

The SWaFUs aren't exactly mutinying, but, like everyone who tries to mount an expedition here, they've been intimidated by China's arcane, overlapping bureaucracy, which traditionally charges Western outfitters exorbitant fees for one-time descents. The Chinese police, for example, have stopped the guides at put-ins and take-outs all over Yunnan, once demanding $80,000 to let Jed and some friends put in on the Irrawaddy. (They left.) The short-term response is to smile, wave, and keep floating. The long-term plan, another goal of these Mountain Travel Sobek expeditions, is to set up a more orderly system of permits.

I'm sharing a ride with Dragon and Mr. Exercise on Willie Kern's raft. During a long, tame drift, he lets biceps-laden Mr. Exercise, who also works as a mountain guide, practice on the oars, which gives him a chance to huddle in the back with Dragon. Willie explains, again, the official permits they do have, on both the local and provincial level, and, more important, the group's guanxi—connections. Through Ed Norton and the Nature Conservancy, the guides have forged close ties to provincial and Beijing officials. Jed, with his Mandarin, has made contacts throughout Yunnan. And Willie, as a Patagonia ambassador, brings a measure of Western exposure.

Foreigners, Willie explains to Dragon, are merely a demonstration technology: As more local guides learn the trade, Chinese companies will lead trips, build boats, and provide services. Chinese clients will follow. When Chinese people are actively invested in protecting these rivers, some of the dams may be prevented, and the whole business of getting permits and running trips will become easier. Willie calls this the "Nepal model," after that country's transition from foreign to local whitewater outfitting in recent years. In 25 years, he explains, American rafters will be gone from Yunnan, outcompeted by Chinese rivals.

This new constituency is already appearing. Universities across China have sprouted clubs for travel, ecology, and mountain climbing. Adventure sports have taken off, and companies that once merely assembled outdoor gear for American companies are beginning to design, build, and market for themselves. China's rising middle class has time and money for leisure activities, and the arrival of the Olympics in 2008 is turning attention toward sports like mountain biking and kayaking. Outside itself launched a China edition in 2006.

Dragon is one of these new Chinese, young enough to see the river as a lure, not a threat. After Willie's patient talk, he sets down his rebellion to take up the sweeps and gets us through the next rapids, albeit backwards.