"I first sailed the Yangtze in 1983 on the Kun Lun, a foreign-leased cruise ship that went back and forth in seedy glamour between Shanghai and Chongqing. Over the next years, I made many trips along China's longest river, most often on its upper reaches, the section between western Hubei province and central Sichuan province in which the Three Gorges, a spectacular 120-mile stretch of mountains, ravines, and once deadly currents, are located. On board ship, I lectured to foreign tourists about Chinese history, shepherded them in and out of museums and factories, took them to hospitals, and...