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Electricity from Hydropower

Hydropower is considered a renewable energy resource because it uses the Earth's water cycle to generate electricity. Water evaporates from the Earth's surface, forms clouds, precipitates back to earth, and flows toward the ocean.

The movement of water as it flows downstream creates kinetic energy that can be converted into electricity. A hydroelectric power plant converts this energy into electricity by forcing water, often held at a dam, through a hydraulic turbine that is connected to a generator. The water exits the turbine and is returned to a stream or riverbed below the dam.

Hydropower is mostly dependent upon precipitation and elevation changes; high precipitation levels and large elevation changes are necessary to generate significant quantities of electricity. Therefore, an area such as the mountainous Pacific Northwest has more productive hydropower plants than an area such as the Gulf Coast, which might have large amounts of precipitation but is comparatively flat.

Environmental Impacts

Although hydropower has no air quality impacts, construction and operation of hydropower dams can significantly affect natural river systems as well as fish and wildlife populations. Assessment of the environmental impacts of a specific hydropower facility requires case-by-case review.

Although power plants are regulated by federal and state laws to protect human health and the environment, there is a wide variation of environmental impacts associated with power generation technologies.

The purpose of the following section is to give consumers a better idea of the specific ecological impacts associated with hydropower.

Air Emissions

Hydropower's air emissions are negligible because no fuels are burned. However, if a large amount of vegetation is growing along the riverbed when a dam is built, it can decay in the lake that is created, causing the buildup and release of >methane, a potent greenhouse gas.

Water Resource Use

Hydropower often requires the use of dams, which can greatly affect the flow of rivers, altering ecosystems and affecting the wildlife and people who depend on those waters.

Often, water at the bottom of the lake created by a dam is inhospitable to fish because it is much colder and oxygen-poor compared with water at the top. When this colder, oxygen-poor water is released into the river, it can kill fish living downstream that are accustomed to warmer, oxygen-rich water.

In addition, some dams withhold water and then release it all at once, causing the river downstream to suddenly flood. This action can disrupt plant and wildlife habitats and affect drinking water supplies.

Water Discharges

Hydroelectric power plants release water back into rivers after it passes through turbines. This water is not polluted by the process of creating electricity.

Solid Waste Generation

The use of water to create electricity does not produce a substantial amount of solid waste.

Land Resource Use

The construction of hydropower plants can alter sizable portions of land when dams are constructed and lakes are created, flooding land that may have once served as wildlife habitat, farmland, and scenic retreats. Hydroelectric dams can cause erosion along the riverbed upstream and downstream, which can further disturb wildlife ecosystems and fish populations.

Hydroelectric power plants affect various fish populations in different ways. Most notably, certain salmon populations in the Northwest depend on rivers for their life cycles. These populations have been dramatically reduced by the network of large dams in the Columbia River Basin.1 When young salmon travel downstream toward the ocean, they may be killed by turbine blades at hydropower plants. When adult salmon attempt to swim upstream to reproduce, they may not be able to get past the dams. For this reason, some hydroelectric dams now have special side channels or structures to help the fish continue upstream.


In the United States, hydropower generates nearly nine percent of the total electricity supply. In the Pacific Northwest alone, hydropower provides about two-thirds of the region's electricity supply.2 Currently, facilities in the U.S. can generate enough hydropower to supply electricity to 28 million households, which is equivalent to about 500 million barrels of oil. In 2003, total hydropower capacity in the United States was 96,000 MW.3 The undeveloped capacity for the United States is approximately 30,000 MW.4

  1. U.S. Department of Energy, Energy Efficiency and Renewable Energy Network, Hydropower Topics.
  2. U.S. Department of Energy, Hydropower Program, Hydropower: Partnership with the Environment
  3. Energy Information Administration, Electricity Generating Capacity, 2002-2003.
  4. U.S. Department of Energy, Hydropower Program, Undeveloped Hydropower Potential by State.

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