How do large dams affect rivers and the environment?
The damming of great rivers is among the most dramatic, deliberate impacts that humans have on their natural environment. Nothing alters a river as totally as a dam. A dam is an attempt to bring a river under control, to regulate its seasonal pattern of floods and low flows. A dam traps sediments and nutrients, alters the river’s temperature and chemistry, and upsets the geological processes of erosion and deposition through which the river sculpts the surrounding land. Such changes can throw an entire watershed out of ecological balance. More than 45,000 large dams now block most big river systems. Dams now hold back 15% of the world’s annual freshwater runoff. If we want to sustain the world’s biodiversity and riverine goods and services, then we need to replace large dam building with alternate solutions. • Read more about the Environmental Impacts of Dams.
