Hydropower, in which the power of moving water – rivers, streams and ocean tides – generates electricity, is the provider of 16% of the world’s electricity and 7% of America’s. Until 2019, it was America's largest source of clean, renewable electricity — when wind surpassed it — generating power in all but two states and accounting for 52% of the nation's renewable electricity generation.

Most hydroelectricity is produced at large dams (called Impoundment Facilities) built by the federal government, and many of the largest hydropower dams are in the western United States, the majority in California, Washington and Oregon. The oldest dates back to 1882, when the world’s first hydroelectric power plant began operating in the United States along the Fox River in Appleton, Wisconsin. The biggest is the Grand Coulee Dam on the Columbia River in Washington, a state that gets about two-thirds of its electricity from hydropower. New York has more capacity than other states east of the Mississippi, followed by Alabama.

A typical hydroelectric plant is a system with three parts: a power plant where the electricity is produced, a dam that can be opened or closed to control water flow, and a reservoir where water is stored. The water behind the dam flows through an intake and pushes against blades in a turbine, causing them to turn. The turbine spins a generator to produce electricity (the amount of electricity that can be generated depends on how far the water drops and how much water moves through the system). It then gets transported through long-distance electric lines to homes, factories, and businesses.

There are other types of hydropower plants, which make use of the flow through a waterway without a dam (called Diversion Facilities) and Pumped Storage. Eighteen states have pumped-storage hydroelectric plants. These generate electric energy during peak load periods by using water previously pumped into an elevated storage reservoir during off-peak periods when excess generating capacity is available to do so. As additional generating capacity is needed, the water can be released from the reservoir through a conduit to turbine generators located in a power plant at a lower level.

Hydropower has significant advantages. Once a dam has been built and the equipment installed, the energy source — flowing water — is free and essentially clean, an energy source renewed by snow and rainfall. Hydropower plants can supply large amounts of electricity, and they are relatively easy to adjust for demand by controlling the flow of water through the turbines.

But there are some disadvantages, too. A dam that creates a reservoir, for example, may obstruct fish migration and affect the ecology of the river, having negative effects on native plants or animals, not to mention people who might have to be relocated. The manufacturing materials, particularly cement, needed also pose a problem because of the carbon emissions associated. And dam failure can be both disastrous and deadly.

Furthermore, the promise of carbon-free electricity from hydropower has been undermined by revelations that decaying organic material in reservoirs releases methane, a potent greenhouse gas that contributes to global warming.

As the controversy continues, global warming, the very condition hydropower wants to combat, has also become its adversary as drought dries up water sources.

Research continues on ways to make hydropower projects more friendly to the ecosystems around them. In some places, small hydro projects can take advantage of existing water flows or infrastructure. Special water intakes and turbines can help make sure the water released from the dam is better aerated to address the problem of low dissolved oxygen. Dams can be planned more strategically to allow fish passages, for example, while water flows at existing dams can be calibrated to give ecosystems more recovery time from flooding cycles.

Tidal and wave power are also being explored. Tidal turbines look similar to wind turbines. They can be placed on the sea floor where there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines have to be much sturdier and heavier than wind turbines. Tidal turbines are more expensive to build than wind turbines but capture more energy with the same size blades. A demonstration tidal turbine project is planned for deployment into the East River of New York in the autumn of 2020.

Ocean waves also contain tremendous energy. It is estimated that harnessing just two one-thousandths of the oceans’ untapped energy could provide power equal to current worldwide demand.

Then there is ocean thermal energy (OTEC), a process or technology for producing energy by harnessing the temperature differences (thermal gradients) between ocean surface waters and deep ocean waters.

The United States became involved in OTEC research in 1974 with the establishment of the Natural Energy Laboratory of Hawaii Authority. The laboratory is one of the world's leading test facilities for OTEC technology. The laboratory operated a 250-kilowatt (kW) demonstration OTEC plant for six years in the 1990s. The United States Navy supported the development of a 105 kW demonstration OTEC plant at the laboratory site. This facility became operational in 2015 and supplies electricity to the local electricity grid.

The Department of Energy estimates there are nearly 50 gigawatts of untapped hydropower potential, according to the 2020 Hydropower Status Report, and that the existing infrastructure provides reliable electricity amid intermittent renewables like solar and wind.


Emissions hit a record high in 2023. Blame hydropower.

By Casey Crownhart 03/07/24
Hydropower is a staple of clean energy—the modern version has been around for over a century, and it’s one of the world’s largest sources of renewable electricity.
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Native American tribes gain new authority to stop unwanted hydropower projects

By Michael Phillis 02/23/24
Federal regulators have granted Native American tribes more power to block hydropower projects on their land after a flurry of applications were filed to expand renewable energy in the water-scarce U.S. Southwest.
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Boiling Point: Are dams good or bad?

By Sammy Roth 01/23/24
The latest forecast has arrived for the West’s largest reservoir — and, stop me if you’ve heard this one, it’s not great.
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‘Not out of the woods’: Lake Mead water levels projected to drop by 2025

By Alan Halaly 01/19/24
Lake Mead, the source of almost 90 percent of Southern Nevada’s water, is expected to near 2022’s historic low by the end of 2025, this month’s Bureau of Reclamation projection shows.
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Is hydropower good or bad for the environment? We went to Idaho to find out

By Sammy Roth 09/28/23
What’s more important: Tearing down dams that have decimated rivers and driven salmon and other fish toward extinction? Or letting those dams stay up, so they can keep producing carbon-free electricity that doesn’t worsen the…
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One of America’s reddest states wants 100% green energy — if dams count as green

By Sammy Roth 09/26/23
Deep in the bowels of Idaho’s Brownlee Dam, Neal Lincoln is ready to offer a demonstration. Almost 40 feet below the surface of the Snake River — whose waters originate in Yellowstone National Park, then…
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Green Groups Are Divided Over a Proposal to Boost the Nation’s Hydropower. Here’s Why

By Wyatt Myskow and Kristoffer Tigue 09/01/23
America’s hydropower industry is hoping to reestablish some of its former glory by making itself central to the nation’s transition to clean energy—and it’s turning to Congress for help.
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As the harms of hydropower dams become clearer, some activists ask, ‘is it time to remove them?’

By Kristoffer Tigue 05/15/23
For most of Joey Owle’s life, the Ela Dam was merely part of the landscape—just another feature of the Oconaluftee River as it runs through Whittier, North Carolina.
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Massive snowpack’s summer bonus: Clean, cheap electricity for California

By Paul Rogers 05/09/23
The huge snowpack that has blanketed the Sierra Nevada this winter has done more than end California’s drought and extend ski season. It’s also changing how Californians keep the lights on. With reservoirs full across…
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Is It a Lake, or a Battery? A New Kind of Hydropower Is Spreading Fast.

By Mira Rojanasakul and Max Bearak 05/02/23
For a century, hydroelectric power has been synonymous with gigantic dams — feats of engineering that provide renewable energy but displace communities and destroy ecosystems.
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What’s going on with hydropower?

For decades, hydropower has been most common source of renewable electricity in the world. (In the US, it was passed by wind a few years ago.) Pumped hydro — large hydropower facilities in which water…
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A Maine jury will decide the fate of the embattled CMP transmission line

By Sabrina Shankman 04/07/23
After years of planning, false starts, and a bitterly fought campaign to kill it, the fate of one of Massachusetts’ most important clean energy projects is set to be decided in a Portland, Maine, courtroom…
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Visualizing the World’s Largest Hydroelectric Dams

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Benefits of Hydropower

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Hydropower is energy in moving water

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International Hydropower Association

Our mission is to advance sustainable hydropower by building and sharing knowledge on its role in renewable energy systems, responsible freshwater management and climate change solutions. We recognise that the world is changing, and a…


Prize Winners Design Ways To Make the Most of Hydropower

By Tiffany Plate   01/17/23  
Hydropower has been delivering energy to the United States for more than a century. Now, it has the potential to help usher the nation into a future powered by clean energy. The Hydropower Operations Optimization…
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Hydropower And Water Scarcity: The Growing Climate Risks Of A Climate Solution

By Jeff Opperman   12/16/22  
Even as a scorching, dry summer fades toward winter, the specter of drought has refused to exit the stage. While drought is defined as a lack of water resources–as typified by the historically low levels…
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The forgotten power of water

By Heather O' Brian   10/06/22  
Often overlooked by governments, a lack of effective market mechanism is holding new hydro and pumped storage back STORAGE NEEDS Electricity grids will require larger and longer storage options as the share of variable wind…
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Here’s how Canadian hydropower will power 1 million New York City homes from 2026

By Michelle Lewis |   09/21/22  
The Champlain Hudson Power Express (CHPE), a high-voltage direct current (HVDC) line, will deliver 1,250 megawatts of clean electricity from Canada’s Hydro-Québec, the fourth-largest hydropower producer in the world, to New York City.
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California’s Drought Is So Bad, It’s Going to Slash Hydropower

By Angely Mercado   06/03/22  
There are already signs of a difficult summer to come. Outlooks from the U.S. Energy Information Administration found that hydropower would make up only 8% of the state’s total power generation, down from 15%, if…
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Why hydropower is the forgotten giant of clean energy

By Katie Brigham   06/02/22  
Hydropower is by far the largest renewable worldwide, producing over twice as much energy as wind, and over four times as much as solar. And pumping water up a hill, aka “pumped storage hydropower”, comprises…
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California drought could cut state’s hydropower in half this summer

By Matt Egan   06/01/22  
The severe drought in California threatens to significantly undermine the state's ability to generate hydroelectric power, raising costs for families and driving up planet-warming emissions, according to a federal government forecast.
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Southwest megadrought pushes hydropower to the brink

By Jason Plautz   05/31/22  
As the megadrought gripping the Southwest stretches into its third decade, energy providers are preparing for a future where hydropower is no longer a reliable renewable resource.
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Far from Lake Powell, drought punishes another Western dam

By Sammy Roth   05/12/22  
Water is flowing through two of three hydropower turbines in a blockish building at the base of Flaming Gorge Dam, so I can feel the floor buzzing — vibrations pulsating through my body — as…
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A Fight Over America’s Energy Future Erupts on the Canadian Border

David Gelles   05/06/22  
Hundreds of feet below a remote forest near Hudson Bay, Serge Abergel inspected the spinning turbines at the heart of the biggest subterranean power plant in the world, a massive facility that converts the water…
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Drought Is Threatening Hydropower in the Southwestern US

By Doug Johnson   04/09/22  
NEWS THAT LAKE Powell, a reservoir on the border of Arizona and Utah, is slowly but surely drying up has spread far and wide. Behind the 1,320-megawatt Glen Canyon Dam and power station, Lake Powell…
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Harnessing the energy of the ocean to power homes, planes and whisky distilleries

By William Booth   11/09/21  
Ocean boosters like to compare the kinetic energy stored in the sea to a ginormous oil reserve that’s never going to run dry. It doesn’t matter if the sun shines or the wind blows. The…
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$1.6 billion clean energy investment to extend operating life of Niagara Power Project

During Climate Week, Gov. Kathy Hochul announced completion of a $460 million modernization and life extension effort at the New York Power Authority's Lewiston Pump Generating Plant, and the digitization of the first of 13…
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Plummeting reservoir levels could soon force Oroville hydropower offline

By Julia Wick   07/21/21  
A major California hydroelectric power plant could soon stop generating power amid worsening drought conditions. According to state water officials, the Edward Hyatt Powerplant at Lake Oroville could go offline as soon as August or…
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Extreme Drought Could Shut Down a Hydroelectric Power Plant In California

By Audrey Carleton   07/19/21  
Officials are preparing for the likelihood that California’s record breaking drought will come for its renewable energy stores. The West Coast state, which has been weathering wildfires, 126-year rainfall lows, and a historic heat dome, announced on Friday that it…
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Humboldt river field office to publish the final environmental assessment for the baltazor geothermal development project

The Humboldt River Field Office has published the final Environmental Assessment (EA) for the Baltazor Geothermal Development Project. The project will be located approximately seven miles southwest of Denio near Baltazor Hot Springs next to…
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Plentiful renewable energy is opening up a new industrial frontier

NORRLAND IS THE largest of Sweden’s three historical “lands”. It spans the top half of the country and is sparsely populated, the more so the farther north you go. The few people who live there…
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Newsletter: Can hydropower help solve the climate crisis? This $63-billion plan is banking on it

By Sammy Roth   05/06/21  
Conservationists in California and across the West are deeply skeptical of hydropower, and it’s not hard to see why. There’s a long history of government agencies damming spectacular canyons, choking off rivers, obliterating fish populations…
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New York and New England Need More Clean Energy. Is Hydropower From Canada the Best Way to Get it?

By Ilana Cohen   10/04/20  
Two massive projects, requiring hundreds of miles of transmission lines, have left Indigenous communities in Canada, and some U.S. activists, up in arms.
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New spillgates on the way to replace ones that have reliably served Martin Dam for nearly a century

By Michael Sznajderman   09/29/20  
For nearly a century, the spillgates atop Martin Dam have helped Alabama Power manage the company’s original source of renewable energy: flowing water.
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Is New England’s Biggest Renewable Energy Project Really a Win for the Climate?

By Tara Lohan   09/24/20  
Construction could start soon on New England’s biggest renewable energy project, a 1,200-megawatt-capacity transmission line to deliver renewable energy to Massachusetts customers. The proposed project, New England Clean Energy Connect, has cleared most of its…
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New York’s Hydropower Plan Stirs Concerns Over Impact on Waterways

By Danielle Cruz   08/12/20  
But NYC needs power to replace Indian Point’s nuclear energy without resorting to new fossil-fuel usage.
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Hydro and Geothermal Stocks: The Dark Horses of Green Energy

Wall Street is underestimating hydropower stocks and geothermal stocks. And in the process, they’re giving you a valuable opportunity to profit from one of the most powerful renewable energy sources.
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Global resource potential of seasonal pumped hydropower storage for energy and water storage

By Julian D. Hunt and Yoshihide Wada   02/19/20  
Seasonal mismatches between electricity supply and demand is increasing due to expanded use of wind, solar and hydropower resources, which in turn raises the interest on low-cost seasonal energy storage options.
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Energy Department Renews Commitment to Collaboration on Hydropower Research and Development with Norway

Last week the U.S. Department of Energy (DOE) and Norway’s Royal Ministry of Petroleum and Energy (OED) made a commitment to collaborate on hydropower research and development by signing an Annex to a previously signed…
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America’s ‘First’ Renewable Resource Overlooked as States Embrace Clean Energy

By Malcolm Woolf   01/31/20  
As laboratories of democracy, states deserve a victory lap for enacting renewable portfolio standards that have helped transform our electricity system. But as the original purposes of these laws have been largely achieved, states can…
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The green power source that can do more harm than good

By Paul Hockenos   01/21/20  
Climate change is already wreaking lethal havoc on the world of flora and fauna. So, all hands on deck to save the planet, right? We're behind in the chase and need all the clean energy…
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Moving To The System Scale Can Improve Hydropower

By Jeff Opperman   01/14/20  
Hydropower is the world’s leading source of renewable energy and most hydropower projects generate low-carbon electricity. Yet—as highlighted in a recent op-ed in CNN—hydropower is rarely placed in the bin of virtuous renewables alongside wind…
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Dammed Good Questions about the Green New Deal

By Don Fitz   11/27/19  
Hydroelectric power from dams might be the thorniest issue that proponents of the Green New Deal (GND) have to grapple with. Providing more energy than solar and wind combined, dams could well become the key…
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How hydroelectricity will help power Asia’s future in 21st century

By M Joseph   11/26/19  
It’s tempting to imagine hydropower as a relatively modern phenomenon – born in the 1950s and really taking root only in the 21st century.
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Department of Energy Challenges Innovators to Harness the Power of the Oceans

Today, the U.S. Department of Energy (DOE) announced developments in two new prizes: Waves to Water, which challenges innovators to desalinate water using the power of ocean waves, and the Powering the Blue Economy™ Ocean…
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Climate impact of hydropower varies widely

Hydropower is broadly considered to be much more environmentally friendly than electricity generated from fossil fuels, and in many cases this is true. However, a new study reveals that the climate impact of hydropower facilities…
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DOE Announces US$24.9 Million Funding Selections to Advance Hydropower

Projects were selected across four areas of interest — hydropower operational flexibility, low-head hydropower and in-stream hydrokinetic technologies, advancing wave energy device design, marine energy centers research infrastructure upgrades.
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Analysis of emerging technologies in the hydropower sector

By Ioannis Kougias George Aggidis   10/01/19  
The paper reviews recent research and development activities in the field of hydropower technology. It covers emerging and advanced technologies to mitigate flow instabilities (active and passive approach) as well as emerging magneto-rheological control techniques.…
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Montana Developer Ready to Build Modern-Day Pumped Hydro Storage

By Julian Spector   08/13/19  
A former Navy prosecutor turned Montana-based clean energy developer wants to build the first pumped hydro storage facility the U.S. has seen in years. Battery installations are growing at a steady clip, but good old…
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US Wind To Exceed Hydropower In 2019 For First Time

By Joshua S Hill   01/16/19  
The latest energy and electricity forecasts from the US government has predicted that wind energy will outperform hydropower for the first time, providing a greater share of the country’s electricity mix in 2019.
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Los Angeles Wants To Use The Hoover Dam As A Giant Battery

By Anthony F. Arrigo   08/29/18  
Los Angeles is looking into whether it should spend an estimated US$3 billion on a massive, 20-mile underground pumped hydropower storage system that would be connected to the iconic Hoover Dam on the Colorado River…
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The Costs and Benefits of Hydropower

By Lois Parshley   01/05/18  
On an early spring evening in southwestern Albania, Taulant Hazizaj walks between silver-gray olive trees near the Vjosa River. Farms sprawl over the wide river valley, swatches of irrigated green giving way to the rocky…
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The Interior Secretary Wants to Enlarge a Dam. An Old Lobbying Client Would Benefit.

By Coral Davenport   09/28/19  
The project is going forward now, in a big win for a powerful consortium of California farmers that stands to profit substantially by gaining access to more irrigation water from a higher dam and has…
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