How Many States Have Hydropower Plants?

How many states have hydropower plants?

Hydropower is the generation of electricity using flowing water. It is a renewable source of energy since it relies on the water cycle to continuously replenish water supplies. Hydropower is an important source of clean, emissions-free electricity generation around the world. In the United States, hydropower is the largest source of renewable electricity, providing over 7% of total electricity generation and 46% of generation from renewables. With growing concerns about climate change and the need to transition to low-carbon energy sources, hydropower offers a reliable way to add more renewable energy to the grid.

The Department of Energy defines hydropower as “the process of using turbines to transform the energy in flowing water into electricity” ( Unlike fossil fuel plants, hydropower does not burn fuel, so it produces no air pollution or greenhouse gas emissions. This makes it a sustainable way to meet energy needs. The United States is the fourth largest producer of hydroelectricity in the world, so examining the role of hydropower nationally can provide important insights into renewable energy development.

Brief History of Hydropower in the US

The use of hydropower in the United States dates back to the 19th century. One of the first hydroelectric power plants was built on the Fox River in Appleton, Wisconsin in 1882 [1]. Hydropower grew steadily in the early 20th century. Major projects like the Niagara Falls plant in 1895 and Hoover Dam in 1936 helped drive growth [2]. By 1920, 40% of U.S. electricity came from hydropower. Massive dam building projects in the 1930s-1960s further expanded hydropower capacity. The share of U.S. electricity from hydropower peaked at nearly 50% in the 1940s before other energy sources began to grow [3].

Hydroelectric Power Generation

Hydropower plants generate electricity by using the energy of flowing water to spin a turbine connected to a generator. Here’s how it works:

  1. Water from a reservoir flows through an intake screen, which filters out large debris.
  2. The water travels through a large pipe called a penstock.
  3. As the water reaches the bottom of the penstock, it pushes against and spins blades in the turbine, like a pinwheel.
  4. The spinning turbine turns an electromagnetic generator, which produces electricity.
  5. The electricity is sent to a transformer to increase the voltage.
  6. From there, the electricity goes to transmission lines that carry it to homes, business, and other end users.

The amount of electricity that can be generated depends on the volume of water flow and the vertical distance the water falls. Greater water flow and height result in more electricity generated. Hydroelectric plants range in size from small systems producing just a few kilowatts to mega facilities generating over 10,000 megawatts.

According to the U.S. Energy Information Administration, hydropower was responsible for generating around 7% of total U.S. electricity in 2021. It’s a renewable power source that offers the flexibility to increase or decrease generation quickly as electricity demand changes.

Types of Hydropower Plants

There are three main types of hydropower plants – run-of-river, impoundment, and pumped storage (U.S. Department of Energy,

Run-of-river hydropower plants channel a portion of a river’s water through a canal or penstock to spin turbines and generate electricity. Unlike impoundment facilities, run-of-river plants do not require dams or water storage reservoirs. They rely solely on a river’s natural flow and elevation drop to generate power (International Hydropower Association,

Impoundment facilities use a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level (Enel Green Power,

Pumped storage plants pump water from a lower reservoir to an upper reservoir when electricity demand is low. During periods of high demand, power is generated by releasing the stored water back down to the lower reservoir through a turbine. Pumped storage allows energy from the turbines to be stored and used when needed (U.S. Department of Energy,

Environmental Impacts

While hydropower provides clean, renewable energy, there are some potential negative environmental impacts. The operation of hydropower plants can affect wildlife, aquatic habitats, and water quality (1).

Building dams and reservoirs for hydropower plants can flood areas that were once wildlife habitats and agricultural land. This can destroy forests and displace both aquatic and land animals from their natural homes (1)(2).

Hydropower dams and reservoirs may also impact the quality of water in the rivers. The slow-moving water in reservoirs absorbs more heat from the sun, which can increase water temperatures downstream. Reservoirs can also reduce oxygen levels in the water, and cause algal blooms from excess nutrients (1).

The changes to river flows from dams can negatively impact native fish populations like salmon that rely on steady flows and cool water for their migration patterns and spawning. Fish can also get injured or killed passing through hydropower turbines (1).

Overall, while hydropower can provide clean energy, the dams and reservoirs built for plants can substantially alter natural habitats and disrupt ecosystems. Careful planning is needed to reduce the environmental impacts.

Number of Hydropower Plants by State

The top 5 states by number of hydropower plants are:

  1. New York – 205 plants [1]
  2. California – 189 plants [2]
  3. Oregon – 166 plants [3]
  4. Washington – 162 plants [1]
  5. Idaho – 132 plants [2]

New York has the most hydropower plants at 205, followed closely by California with 189 plants. The Pacific Northwest states of Oregon, Washington, and Idaho round out the top 5 with over 160 plants each. Hydropower is an important source of renewable energy across many states.

Hydropower Generation by State

The top 5 states for hydropower generation in megawatts are:

  1. Washington – over 80,000 MW of capacity (
  2. Oregon – over 15,000 MW of capacity (
  3. California – over 15,000 MW of capacity (
  4. New York – over 5,500 MW of capacity (
  5. Idaho – over 3,000 MW of capacity (

The Pacific Northwest region, including Washington, Oregon and Idaho, contains the largest concentration of hydroelectric dams in the United States due to the Columbia River basin and other large river systems ideal for hydropower generation.

Recent Expansions

In recent years, there has been renewed interest in expanding hydropower capacity in the United States. According to the U.S. Department of Energy’s vision report, hydropower could grow from 101 GW of capacity in 2015 to nearly 150 GW by 2050.

Some notable new hydropower projects in the U.S. include the Red Rock Hydroelectric Project in Iowa, which opened in 2015 as the first new hydropower plant in the U.S. in over 30 years. In 2016, the Wanapum Dam Hydroelectric Project opened in Washington state with advanced hydropower technology funded by the Department of Energy. And in Maine, construction started in 2020 on the Brookfield Hydro Project, which will be the state’s largest hydro facility.

Going forward, most new hydropower projects are expected to be small-scale, low-impact designs like small hydrokinetic turbines and conduit power plants. But large-scale expansion is still possible, especially at existing dams and infrastructure.

Future Outlook

Hydropower has significant potential for future growth in the United States. According to the Hydropower Vision report by the Department of Energy, under a modeled growth scenario, hydropower capacity could nearly double by 2050, reaching nearly 150 GW (1). This growth will come from upgrading existing hydropower infrastructure, powering existing non-powered dams, and developing new stream-reach development (2).

However, there are also several challenges facing future hydropower growth. Environmental concerns around dam construction can make permitting difficult. Droughts and changes in precipitation patterns driven by climate change may impact electricity generation at some facilities. Upgrading existing infrastructure can be costly, as much of it is decades old. Lastly, competition from other renewables like wind and solar will continue to play a role in determining future hydropower investments (1).

Overall, hydropower is poised for moderate growth in the coming decades if challenges around permitting, droughts, and aging infrastructure can be adequately addressed. The Department of Energy and the hydropower industry will need to continue innovating and investing to realize the full growth potential. However, hydropower’s unique ability to provide reliable, flexible baseload power will ensure it remains an important part of the nation’s renewable energy portfolio (2).

1. A New Vision for United States Hydropower

2. Hydropower Vision: New Report Highlights Future of US Hydropower


In summary, hydropower is an important renewable energy source in the United States. As of 2022, there were 2,198 active hydropower plants across 34 states, generating nearly 7% of the nation’s electricity annually. The top hydropower producing states are Washington, Oregon, California, and New York. While most major potential dam sites have already been developed, some expansion is still possible by adding power facilities to existing dams and canals.

Hydropower offers some notable advantages, including renewable baseload power with minimal carbon emissions. Upgrading existing infrastructure can also increase efficiency and capacity. However, hydropower does alter local ecosystems and waterways, so environmental impacts must be carefully managed. With most suitable dam sites already in use, growth of hydropower will be constrained compared to other renewables like wind and solar. Nonetheless, existing hydropower facilities will continue providing clean electricity and grid reliability for decades to come.

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