The 30 Largest Hydropower Plants in the U.S.

Did you know that the largest power plant in the United States is hydroelectric?

Hydropower is the second-largest source of U.S. renewable electricity generation and the largest source of power in seven different states.

The above infographic from the National Public Utilities Council charts the 30 largest U.S. hydropower plants and shows how droughts are starting to affect hydroelectricity. This is part one of two in the Hydropower Series.

Dam, That’s Large: U.S. Hydropower Plants by Generation

The top 30 hydropower plants account for around 50% of U.S. hydroelectric generation annually.

Hydropower plants are most prevalent in the Northwestern states of Washington and Oregon, jointly hosting 16 of the top 30 plants.

The Grand Coulee Dam in Washington is the country’s largest power plant. It generates over 19.5 million megawatt-hours (MWh) of electricity annually and supplies it to eight states, including parts of Canada. Overall, 10 of the top 30 hydropower plants are in Washington.

The Robert Moses Power Plant is a close second, located around 5 miles downstream from Niagara Falls. Combined with the nearby Lewiston Pump Generation Plant, it is New York’s single-largest source of electricity.

While hydropower is a relatively reliable renewable power source, prolonged dry conditions can put it at risk. That is the case for both the Glen Canyon and Hoover Dams, which are no longer running at previous capacities.

Running Dry: Water Scarcity and Hydropower

The Southwestern U.S. has been in a “megadrought”—a prolonged drought lasting longer than two decades—since 2000. In fact, it has gotten so severe that the past 22 years mark the region’s driest spell in 1,200 years.

Consequently, many Southwestern reservoirs have below-average storage levels. When these levels fall below a certain threshold, hydropower plants can no longer generate power.

In particular, storage levels are precariously low at Lake Mead (Hoover Dam) and Lake Powell (Glen Canyon Dam), which supply most of Arizona’s hydroelectricity. They are also the two largest reservoirs in the country.

Here’s a look at how filled these reservoirs are as of Dec. 4, 2022:

To put those figures into perspective, here’s an animation looking at Lake Powell’s surface area changes from 2018 to 2022:

Shrinking water levels at reservoirs threaten the reliability of hydropower and the millions of people that rely on it for electricity. As droughts become more frequent due to climate change, what does the future of hydropower look like?

Find out in Part 2 of the Hydropower Series, where we’ll dive deeper into how droughts are affecting dams and how hydropower fits into the bigger decarbonization picture.

Visualizing the State of Climate Change

The recent influx of wildfires, droughts, and hurricanes serves as a warning sign of the impact of climate change.

In order to identify ways to mitigate the crisis, it’s important to understand the historical drivers and current state of climate change.

This infographic sponsored by the National Public Utilities Council (NPUC) explores how human activities have influenced the climate crisis and how decarbonizing the power sector can help.

The Human Drivers of Climate Change

Global warming, the phenomenon driving climate change, is a result of increasing greenhouse gas (GHG) emissions.

GHGs in the atmosphere increase the Earth’s temperature through the greenhouse effect. This refers to the natural warming of the Earth that occurs when GHGs trap the sun’s heat.

Since the Industrial Revolution, human activities like energy generation and consumption from fossil fuels have accelerated GHG emissions and the greenhouse effect. The atmospheric concentration of carbon dioxide is now nearly 415 parts per million (ppm), up from around 280 ppm prior to the Industrial Revolution. As a result, the Earth is warming faster.

For a better understanding of how humans have contributed to the crisis, here’s a look at historical CO₂ emissions by sector:

Electricity and heat by far accounts for the largest share of emissions since 1990. This is because of the dominance of fossil fuels in our energy mix over the last few decades.

The transport sector is the second-largest contributor largely due to the reliance on internal combustion engines, oil-fired ships, and other fossil fuel products like jet fuel.

Limiting the temperature rise and ultimately the impacts of climate change will require emissions reductions across all sectors, starting with electricity generation.

How Decarbonizing the Power Sector Can Help

A decarbonized energy system with clean electricity generation is an essential building block for the road to net-zero emissions.

There are two factors that emphasize the importance of a clean power sector. First, all sectors of the modern economy rely on electricity for daily functions. If this electricity comes from clean sources, it can help reduce the consumer’s carbon footprint. Second, global power demand is charging up with the electrification of sectors like transport and industry. As a result, supplying clean electricity will be more important than ever.

In Part 2 of the Road to Net Zero series, we will explore pathways to decarbonize the U.S. economy, beginning with the power sector.