What effects do dams have on the environment?

The alteration of a river's flow and sediment transport downstream of a dam often causes the greatest sustained environmental impacts. Life in and around a river evolves and is conditioned on the timing and quantities of river flow. read more

The environmental consequences of large dams are numerous and varied, and includes direct impacts to the biological, chemical and physical properties of rivers and riparian (or"stream-side") environments. read more

Some of the environmental effects of dams can benefit some species. For example, impounding a reservoir will create habitat for lake fish and warm water released from a reservoir can increase the abundance of species of fish which failed to thrive in the cool river. read more

Dams have had such an impact on the world that more than half of the world’s major rivers had dams constructed on them by the end of the 20th Century ¹. However, such alterations of nature have not come without great tolls on the environment, such as the wiping out of entire species, flooding wetlands, forests, and farmlands, and displacing millions of people around the world. read more