An image from 15 April 2009 showing the Three Gorges Dam on the Yangtze River and the flooding upriver from the dam. The main purposes for the dam are twofold: to supply water for the largest hydroelectric plant in the world and to help control the devastating floods that plague the lowlands downstream from the dam. The epic scale of the dam project is matched by the level of controversy it continues to generate. Concerns about major environmental impacts, the relocation of 1.3 million people, and the flooding of 13 cities, more than 1,300 villages, archeological locations, and hazardous waste dumps were raised throughout the planning and implementation. Environmental concerns include increased seismicity from the loading of the water, landslides, changed ecosystems, accumulated pollution, increased chances for waterborne diseases, and salinity changes in the Yangtze estuary. Photo courtesy of NASA.