The Yangtze River -- the world's third-longest and China's main waterway -- begins in the Tibetan plateau and travels eastward across China, providing fresh water for 400 million people before emptying into the East China Sea at Shanghai.
Some of China's thorniest environmental problems are centered on its great rivers, which have been battered by massive damming, pollution, and habitat change. Here, Chinese policemen navigate a lake near the Zipingpu Dam, littered with debris from the May 12, 2008, earthquake in Sichuan province.
The Yangtze is prone to flooding -- one of the problems that Chinese water-control projects are supposed to help remedy. In this photo from September 6, 2008, the river approached the 25-meter (about 80-foot) flood line near the city of Wuhan in central China's Hubei province. This part of the country experiences heavy rain every summer, which is why the Three Gorges Dam was designed to withstand floods so intense they only happen every 10,000 years.
The dam prepares for serious flooding by closing its navigation locks during the peak flow period, which diverts water pressure to the reservoir upstream.
Floods this past summer provided the Three Gorges Dam with its greatest test since the completion of its construction. On July 20, the volume of water hitting Three Gorges reached about 70,000 cubic meters per second -- some of the fastest flowing floodwaters in over a decade. Authorities scrambled to evacuate those located along the flood's path, piled sandbags along the Yangtze's banks, and worked to drain reservoirs. The rains were abnormally heavy -- the Yangtze basin had 15 percent more rainfall in 2010 than in an average year.
Here, a Chinese worker cleans up debris of some of the buildings demolished by the floods in Wuhan on July 27.
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