He clearly had such adventures in mind when he bought his vehicle, a primordial two-wheel-drive suv made by the Great Wall Motor Company. Having reached Beijing’s Tong Hui canal, Mr. Zhang gleefully bounced us down a dirt path overlooking it. On one side were the makeshift settlements of some of Beijing’s legions of migrant laborers, and on the other, the cement-lined, nearly waterless channel. Mr. Zhang pointed to a slightly viscous liquid issuing from a foot-wide pipe on the opposite bank and declared that this marked the first entrance of raw sewage into the canal; from this point on, he said, all the sewage entering the channel, including the squatters’ own waste, was untreated. Far downstream, the canal’s water merges with the Hai River, one of China’s mostthe eia calls “the wood flooring centre of the world,” with more than 500 flooring factories.

Until 1998, China fed its wood mills trees from its own forests. That year, the middle reaches of the Yangtze River swelled with the region’s biggest flood in more than 50 years, killing 3,000 people, destroying 5 million homes, and engulfing 52 million acres of land. As winter approached months later, 14 million were still homeless. The land, it turned out, had no defense against erosion left. Lakes and wetlands that once would have absorbed some of the rain had been drained to create farmland, and the forests that once held topsoil in place had been harvested. Torrential rainwater carried the topsoil to the river and then down it, until its bed swelled