It could be argued that nowhere has the impact of dams on rivers been more important than in China, where since 1950 almost half of the world's large dams (higher than 15 meters) have been built ]Fuggle and Smith, 2000]. China's Yangtze River (Changjiang)—the largest river in south Asia (1.8 million square kilometers) and whose basin is home to more than 400 million inhabitants—alone has more than 50,000 dams within its watershed, including the world's largest, the Three Gorges Dam (TGD) (Figure 1a ).

Water and sediment began being impounded behind the TGD in June 2003, and two years after impoundment, river sediment discharge downstream (at Datong Station) had decreased by nearly half of its 2002 load (Figure 1c). However, the decrease in Yangtze sediment load did not begin with TGD impoundment. Rather, the sediment load at Datong has declined continually since 1987 despite a slight increase in river discharge (Figure 1c ). The change in pre-TGD loads atYichang, just downstream from the TGD, has been even more extreme, decreasing by approximately 300 million tons in 1986–2002, before declining another 130 million tons after 2002 (Figure 1b). All of this suggests that collective changes on the Yangtze upstream (above Yichang) have been more important in decreasing the river's sediment load than the TGD.