You are reading Part 3 of 7 in this series. What are Quick Facts?

Hydropower made up 2.7% of the energy (and 23% of renewable energy) used in the United States in 2018 and 6.7% of electricity generated in the United States in 2019.

What is hydropower and how is it used?

  • Hydropower is generated by the force of moving water, and there are several types of hydropower facilities. Often, flowing water turns blades in turbines, which spin generators to produce energy.

  • Other systems can generate energy from ocean currents, tides, and waves, although these technologies are less common and not always included in the category of hydropower.

  • Hydropower technology to generate electricity originated in the late 1800s, (although water wheels were used to perform work long before that). Hydropower infrastructure such as dams and turbines produced over 40% of U.S. electricity during the early 20th century. With the growth of other technologies, it now represents a much smaller fraction of U.S. energy, but sites like the Hoover Dam and Niagara Falls continue to generate hydropower.

What are the advantages and disadvantages of hydropower?

  • The cost of hydropower varies, but compared to other energy options, it is a relatively low-cost source.

  • Many hydropower facilities can also store energy by pumping water upwards so it can be released to turn turbines and generate electricity when needed.

  • The energy output of many hydropower facilities can be quickly ramped up or scaled down to increase the reliability and flexibility of energy systems. This is an upside — allowing less consistent forms of renewable energy to be added to the grid. However, hydropower generation faces regulatory and operational constraints that limit this flexibility.

  • The average age of U.S. hydropower dams is now around 60 years, and aging infrastructure carries increased risk of failure and harm to surrounding areas.

  • Hydropower facilities like dams and turbines often interfere with ecosystems. For example, the migrations of water animals can be disrupted, and the biochemical balance of marine environments can be altered.

  • Decomposition of organic matter in reservoirs produces greenhouse gases, primarily methane, whose quantities are not yet precisely calculated.

  • Reservoirs are estimated to produce about 1.5% of global human-caused emissions of carbon dioxide, methane, and nitrous oxide. However, greenhouse gas emissions  per unit of energy generated vary greatly at different facilities based on such variables as local ecology and generation technology; some emit at rates as low as clean-energy sources like wind, while others emit at rates several times higher.


  1. Researchers evaluate the efficiency and environmental impact of U.S. hydropower facilities in the 2019 article from Renewable and Sustainable Energy Reviews, Status, trends and significance of American hydropower in the changing energy landscape. A 2016 analysis in Bioscience, Greenhouse Gas Emissions from Reservoir Water Surfaces: A New Global Synthesis, explains how greenhouse gases emerge from reservoirs and gathers data to quantify the emissions. Life cycle greenhouse gas (GHG) emissions from the generation of wind and hydro power, a 2011 article from Renewable and Sustainable Energy Reviews, details the ways wind and hydropower technology generate emissions and contextualize these effects through comparisons to emissions from other forms of energy production. A 2018 review from Ocean Engineering offers updates on the potential of various technologies that harness energy from oceans.

All Renewables:

  1. The Energy Information Administration (EIA), an independent federal agency, provides an overview of energy in the United States, explains energy sources and uses, and answers common questions about renewables and other forms of energy. It also offers a wealth of data about energy generation and consumption from different sources over time and publishes news and analysis about energy and related policy. The EIA’s Annual Energy Outlook 2020 with projections to 2050 outlines how energy generation and use may change in the future, based on markets and historical trends.

  2. The Business Council for Sustainable Energy’s 2020 Sustainable Energy in America Factbook includes recent information on the U.S. energy sector, such as market details, data on emerging technologies, and historical trends.

  3. The U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) published the 2018 Renewable Energy Fact Book, which is the most recent edition and includes summary information on the different types of renewable energy sources. The Fact Book was prepared by the National Renewable Energy Laboratory, which also gives information about each of the major renewable energy sources. The EERE also describes technologies and research in different methods of renewable electricity generation, including solar, geothermal, wind, and water.

  4. The U.S. Environmental Protection Agency’s Energy and the Environment resource delves into the environmental effects of energy systems and provides tools to measure environmental impact.

  5. The International Energy Agency (a Paris-based autonomous intergovernmental organization) produced the report Global CO2 Emissions in 2019, which provides helpful international context about global energy trends and development. A report from the International Renewable Energy Agency (IRENA), Renewable Power Generation Costs in 2019, breaks down the prices tied to different renewable energy technologies and processes on a global scale.