Slated for completion in 2009, the Three Gorges Dam will be the largest hydroelectric dam in the world. The dam is located near Sandouping, China in the Qutang, Wu and Xiling Gorges on the Yangtze River, the third largest river in the world. This fifteen year construction project has been hailed as the modern Great Wall. Planning for the project began in 1970 and construction started in 1994. Some of the power plants as well as the five-lock ship passage became operational in 2003, and the remainder will be operational in 2009.
The dam is 590 ft. (180 m) high and 7,050 ft. (2150 m) wide. It has 26 turbines capable of generating 18.2 gigawatts of electricity dwarfing Itaipu's output of 13.3 gigawatts and Grand Coulee's of 10.8 gigawatts.
The secondary advantage of this dam is its ability to control flooding. The Yangtze, being one of the world's largest rivers, draining 700,000 square miles (1,800,000 km2), floods every year. The devastation of these floods varies, but on a particularly bad year, tens of thousands are killed and millions are left homeless. The dam is expected to drastically improve living conditions downstream. However, it is still uncertain if the dam will truly have this effect.
This project has come with a cost much greater than the US$25 billion (the low estimate, US$75B is the high estimate) spent on its construction. The 420 square mile (1090 km2) reservoir will submerge 300,000 farms, 13 major cities, 140 major towns, 1700 small villages, and 1300 archeological sites. Farmers have been forced to relocate from the once feral land to areas now over crowded and not as adequate for agriculture. Also, they were not educated on how or provided with necessary technologies to work the new land.
I really don't want to get into China's environmental policies, but this dam falls right in line with them. Basically their stance is, the environment be damned, we are going to develop our country, citing this is the same attitude displayed by the Europe and the United States in the 20th century. An enormous amount of pollution is expected to accumulate in the dam's reservoir. The river's "natural ability to purify itself from pollutants, discharges from more than 3,000 nearby factories and mines" will be hampered by the dam. Of course it doesn't truly purify anything, it merely pushes it out into the East China Sea.
Sources:
http://www.welcome-to-china.com/biz/fyi/68p.htm
http://www.chinadam.com/dam/facts.htm
http://www.american.edu/ted/THREEDAM.htm