One mile long and 600 feet high, the Three Gorges Dam on the Yangtze River is a project of epic proportions — and controversy. The dam, completed in 2008, created a vast reservoir extending 370 miles, about the distance from Los Angeles to San Francisco. It brings drinking water to northern China and generates as much electricity as 18 coal-fired power plants. But it has also displaced some two million people and caused widespread flooding, destroying rural villages and cultural treasures.