Scaturro was more envious of the adventure than horrified by the tragedy. "I thought, My God, that's the greatest story I ever heard. I was so fucking jealous."

After graduating in 1980, Scaturro moved to Denver and went to work for Amoco as a geophysicist. After four years, he struck out on his own, taking lucrative consulting jobs that left him with enough freedom and money to take off on adventures. During an ascent of Argentina's 22,834-foot Aconcagua, he found himself at Camp 1, two miles ahead of his teammates. To kill time, he made tea and organized the camp himself.

"I decided most mountaineers didn't know shit about logistics and organizing expeditions," he says, "so I started doing it myself." He guided friends on Aconcagua twice more before trying the Himalayas, the Karakoram, and high-altitude peaks in Russia and Alaska, including Mount McKinley. He led private rafting expeditions as well, running some of the same rivers Sobek had pioneered.

For his first Bío-Bío trip, Scaturro borrowed Sobek oar boats, customized them with raft frames he designed himself, and ran the river Grand Canyon style. He helped produce an ESPN film about the Bío-Bío in 1991, to raise awareness of the dam projects that were about to ruin it. "If God created the perfect river," he told me, "it was the Bío-Bío."

I took that as a figure of speech, since the only other time I'd heard Scaturro use the word God on our expedition had been with damn. I never would have guessed he used to be a churchgoing man-a Baptist deacon, no less. But he and his first wife had been devout Christians, both raised in deeply religious families. (Growing up in Hollywood, Scaturro shared a bedroom with four brothers in a bungalow behind his father's Sunset Boulevard trattoria, Vince's Little Star Restaurant, which was right near Paramount Studios.) His marriage broke up after 17 years, in 1989. His wife's spiritualism had grown increasingly fervent, he says, to the point that it interfered with their relationship. He'd been donating heavily to the church but stopped when he suspected the elders were scamming him in a building project, quit the congregation, renounced organized religion, and split with his wife. "I feel like I had to go through that period," he says.

Relaxing in camp on the Omo one evening, Scaturro said, "When you take away the guilt trip of religion and knock down the walls, you have to ask yourself, 'What are my boundaries?' I get out here and I can see more clearly. It's like being on a straight stretch of river."

Mostly, though, Scaturro kept focused on our progress. Every afternoon he would sit at a folding table to update his daily river log and annotate a computer-generated topo map of the river that he'd produced at home. The map was about 15 feet long and 18 inches wide. It showed the river corridor in fine detail but omitted one critical feature: a massive new hydroelectric plant being built about 45 miles below the put-in. It was only after reaching Addis that we'd heard rumors about it. The project is part of the government's scheme to harness every major river in Ethiopia.

On the night before we reached the plant, sitting around the campfire with wine in hand, Scaturro slipped into a reflective mood. "Are the Ethiopian people better off with the dams or not?" he asked. "I don't know."

There was no equivocating the next morning when we rounded the first bend and saw what was happening. Roads that had been bulldozed down from above on both sides of the river were about to converge at the narrowest point in the canyon. The channel was being pinched off by tons of rock debris supporting the ends of a temporary bridge. In a week, the bridge would be finished, the river blocked. Along the right bank was an enormous poured-concrete turbine plant. A second generating plant and a nearly 800-foot-high dam would be located about a hundred miles downstream. By 2011, when both projects are scheduled to be online, the most spectacular part of the Omo Valley will be lost forever.

Scaturro scowled. "There aren't going to be any free-flowing rivers left in the world," he grumbled. "All that will remain is cesspools. We may be the last generation to have these river adventures." As we shot the rapids in the narrowing gap at the bridge site, he roared, "Yahoo, baby! The last run on the Omo!"