Hydropower

Vine Street Hydroelectric Project, Albany, OR

While water itself is a renewable resource, the natural ecology of rivers is not

Hydropower -- energy produced by moving water -- is the largest source of renewable electricity in the United States, accounting for about 6 percent of our electric supply. Over the past century, thousands of important rivers and streams have been dammed to produce hydroelectricity.

While water itself is a renewable resource, the natural ecology of rivers is not. Hydroelectric dams adversely impact aquatic ecosystems by harming plants, fish, and other wildlife in and near rivers. Dam-building peaked in the 1960s in this country, before environmental protection was a consideration. In recent decades, the growth of hydroelectric power has slowed greatly, because most of the "best" sites were already built and environmental laws were enacted.

How Hydropower Works

Most hydroelectric power plants use dams to impound river water in a reservoir, and then release it in a controlled fashion to spin a turbine and generate electricity. Some “run-of-river” facilities operate with just a small dam, but these still divert, or “bypass” a portion of a river. Bypass reaches can be miles long. Other projects simply use water in an existing canal, taking advantage of already available flow.

Where Hydropower Is Used

The first hydropower facility in the country was commissioned in 1882, on the Fox River in Appleton, Wisconsin. By 1940, hydropower accounted for 40 percent of the electricity generated in the country.

Today, more than half of U.S. hydropower is concentrated in the states of Washington, Oregon and California. New York is also a major producer of hydropower. Maine gets 22 percent of its electricity from hydropower.

Environmental Impacts of Hydropower

Most large hydroelectric dams in the United States were built when the impacts of dams on fish, water flow, and the aquatic environment in general were not considered. These dams operated for decades without the safeguards of environmental law.

Large dams physically block migrating fish from reaching their spawning grounds, and the reservoirs impact the flows, temperature, chemistry, and silt loads of a river or stream. These impacts, including the reduction of thousands of miles of fish habitat, specifically of anadromous fish such as salmon, which live in the sea and breed in fresh water, have resulted in drastic decreases in fish populations. Salmon runs in rivers such as the Klamath in Oregon and California, which historically had runs of millions of fish, have been reduced to a fraction of their former abundance.

Dammed reservoirs can also cover important natural or agricultural land, culturally significant sites, and even force people to leave their homes.

Some existing hydropower facilities can be less damaging than others. The Low Impact Hydropower Institute certifies existing facilities according to a number of criteria, including wildlife and watershed protection, cultural resource protection, river flow and water quality.

Learn More


Low Impact Hydropower Institute
The website of this nonprofit has a searchable map and list of certified and pending low-impact hydropower projects, as well as a handbook on how to apply for certification.
Hydropower Reform Coalition
This coalition of non-governmental organizations advocates for better management of existing hydropower dams to ensure protection of rivers and riparian ecosystem.
National Hydropower Association
This trade association dedicated to the expansion of hydropower in the United States provides news, policy, and basic background information.
IEA Hydropower
A global view of hydropower and the issues surrounding it, including news, policy, and technical information, from a working group of the International Energy Agency.
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