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YICHANG, China—According to legend, one of China's ancient emperors—Da Yu, or Yu the Great—changed the course of Chinese history by placing a mountain in front of the Yangtze River, forcing it to flow east through the Middle Kingdom (instead of south like the other great rivers that rise in the same Yunnan region of southwest China). Not to be outdone, the modern Chinese government has undertaken a massive project to control the flow of this ancient waterway, erecting Three Gorges, the world's largest dam, to block it.
View Slide Show of Yangtze River Development
That megaproject, completed in 2006 at a cost of $30 billion (180 billion yuan), has already raised the water level in the upper reaches of the river by as much as 66 feet (20 meters), stretching all the way to the city of Chongqing. As a result, the ubiquitous barges plying the river no longer need human muscle to beat the flow and can carry more than three times as much weight—from 3,000 tons per ship to 10,000 tons of coal, cars and other goods.
The dam also provides 22,500 megawatts of power, without emitting the greenhouse gases and other air pollutants produced by coal-fired power plants that provide more than 75 percent of China's electricity. In addition, the massive dam generates more power than 18 1000 megawatt nuclear reactors as well as protects communities downstream from horrific floods—such as one in 1998, which left 14 million homeless—that once plagued Wuhan, Nanjing and even Shanghai.
"One of the main reasons to build Three Gorges dam [was] to store water in the upper river so as to protect eastern parts of the country," says Lai Hun Suen, a professor of sustainable development at Chongqing University and a municipal government official.
But it came at a cost: More than four million residents of towns, villages and cities in the path of the rising waters were forced to relocate, most of them to bustling Chongqing. What's more, when the water level changes it unleashes a miasma of disease from exposed sewage. The baiji dolphin has also been rendered extinct by a combination of overfishing and habitat destruction caused by human activity.
Environmental challenges could undermine the world's largest dam as well. Silt could gum up the Three Gorges and climate change could completely transform the water supply as the glaciers dwindle atop the Tibetan Plateau, among other issues. And efforts to emulate Da Yu—smaller dams have proliferated in the upper reaches of the river—may yet prove the undoing of the mightiest of man-made waterworks. "We have taken big floods into consideration," Lai says, "what we did not expect is less water."