Five-second answer
Claim we investigated
Hydropower supplies most of Washington's electricity, and Grand Coulee is the largest U.S. power plant.
Mostly true. Hydropower has produced most of Washington's power since 2001; Grand Coulee leads by capacity, not annual output. Federal EIA data show conventional hydropower produced 59.3% to 79.7% of Washington's in-state electricity generation each year from 2001 through 2025, and Washington has led all states in hydro output every year. Grand Coulee Dam has 6,809 MW of nameplate capacity, the most of any U.S. plant. The claim needs two qualifications: nuclear plants produce more electricity each year than Grand Coulee, and on a delivered-to-customers basis hydro was just under half of Washington utilities' 2024 supply.
Quote or cite this fact-check
FactHub rates the claim “Hydropower supplies most of Washington's electricity, and Grand Coulee is the largest U.S. power plant” Mostly true (high confidence): Hydropower has produced most of Washington's power since 2001; Grand Coulee leads by capacity, not annual output. Reviewed October 9, 2026. https://facthub.org/n/article/wa-hydropower-grand-coulee/2
One-minute summary
What the evidence establishes
- Hydro produced 59.3% to 79.7% of electricity generated in Washington each year from 2001 to 2025; it was 63.6% in 2025.
- The share fell to its lowest levels in the 2023 and 2024 drought years (59.7% and 59.3%) and has drifted down over 25 years as wind and gas grew.
- Washington led all states in hydro output every year 2001-2025, with 22.9% to 32.4% of the U.S. total.
- On a delivered-to-customers basis, Washington utilities reported 48.73% hydro in 2024, with 15.44% from unspecified sources.
- Grand Coulee has 6,809 MW of nameplate capacity, the most of any U.S. plant; Vogtle is second with 4,658 MW.
- By electricity produced, Grand Coulee ranked 27th in 2025 (16.2 TWh); Vogtle (37.1 TWh) and Palo Verde (31.3 TWh) led.
The evidence
The conclusion rests on the combined record. Expand each item to see its role and limitations.
| Method | Institution / country | Year(s) | What it shows | Key limitation | Primary links |
|---|---|---|---|---|---|
| Federal census of power-plant generation (Form EIA-923), aggregated by state and energy source | U.S. Energy Information Administration United States | 2001, 2010, 2020, 2023, 2024, 2025 | Conventional hydro supplied between 59.3% (2024) and 79.7% (2011) of Washington's in-state net generation each year from 2001 through 2025, averaging 68.9%. In 2025 it produced 64.7 of 101.7 terawatt-hours (63.6%). The share has drifted down, from an average of 71% in 2001-2010 to 65.1% in 2016-2025, as wind and natural gas grew. | This measures electricity produced by plants in Washington, not electricity used by Washington customers, and EIA compiles both the plant reports and the state totals, so this line depends on one institution. Annual totals hide seasonal swings. | U.S. Energy Information Administration FactHub FactHub |
| Comparison of generation data with independent state drought declarations and federal hydrologic analysis | U.S. Energy Information Administration, Washington State Department of Ecology United States | 2023, 2024, 2025 | The only two years below 60% were 2023 and 2024 (59.7% and 59.3%), when the Department of Ecology declared drought emergencies (12 watersheds in 2023; most of the state from April 16, 2024). EIA reported that 2023 monthly hydro output in Washington, Oregon, Idaho and Montana was near or below the low end of its 10-year range in most months. The share recovered to 63.6% in 2025. | Drought declarations describe water supply, not power output, and the declarations cover watersheds rather than the Columbia River system as a whole; the timing match is descriptive and does not by itself measure how much drought reduced generation. | U.S. Energy Information Administration Washington State Department of Ecology U.S. Energy Information Administration FactHub |
| State compilation of utility fuel-mix disclosures | Washington State Department of Commerce United States | 2024 | Commerce's aggregate 2024 fuel mix for Washington utilities was 48.73% hydro, 15.44% unspecified, 13.33% natural gas, 9.6% wind, 5.91% coal and 5.13% nuclear. Hydro was by far the largest identified source, but in a drought year it was not a majority of what customers received. | One year only. 15.44% of delivered power was "unspecified" (mostly market purchases with no identified source), some of which may be hydro, so 48.73% is a floor rather than an estimate of the true hydro share. The figures are utility-reported resource claims, not metered physical flows, and were transcribed from Commerce's chart. | Washington State Department of Commerce Washington State Department of Commerce FactHub |
| State supply-and-disposition accounting (generation, retail sales, losses and trade) | U.S. Energy Information Administration United States | 2001, 2020, 2022, 2023, 2024 | In-state generation exceeded retail sales in every year from 2001 through 2024 (ratio 1.04 to 1.34); in 2024 in-state hydro alone equalled 67.5% of retail sales. EIA's estimate of net interstate trade shows Washington as a net exporter in most years (21-29 million MWh a year in 2020-2022) but a net importer in 2023 (1,170,693 MWh) and 2024 (385,768 MWh), as it also was in 2001 (10,176,675 MWh) and 2010 (1,279,785 MWh). | EIA computes net interstate trade as a residual that absorbs errors in estimated losses, and physical flows cannot show which plant served which customer. 2025 supply-and-disposition data are not yet published. | U.S. Energy Information Administration U.S. Energy Information Administration FactHub |
| Ranking of state conventional hydro generation | U.S. Energy Information Administration United States | 2001, 2025 | Washington ranked first among states for conventional hydro generation in every year 2001-2025, with 22.9% to 32.4% of the U.S. total. In 2025 it produced 64.7 TWh (26.8%), more than Oregon (28.7 TWh) and California (28.1 TWh) combined. | Credits each dam to the state where it stands; Columbia River output depends partly on water from Canada, Idaho and Montana. | U.S. Energy Information Administration FactHub |
| Census of operable generators (Form EIA-860) summed by plant, checked against the operator's published capacity | U.S. Energy Information Administration, U.S. Bureau of Reclamation United States | 2025 | Summing EIA-860 generators by plant, Grand Coulee has 6,809 MW of nameplate capacity (matching Reclamation's 6,809 MW) and 7,079 MW of net summer capacity, first on both measures. Vogtle (GA) is second on both, with 4,658 MW nameplate and 4,530 MW summer capacity. Excluding Grand Coulee's pump-generating units, its conventional hydro units alone total 6,495 MW. | Plant boundaries follow EIA plant codes. Capacity figures differ by definition: EIA-860 sums to 7,079 MW net summer capacity, while an EIA article cited about 6.7 GW; Reclamation operates the plant and is not independent of it. | U.S. Energy Information Administration U.S. Bureau of Reclamation U.S. Energy Information Administration FactHub |
| Plant-level annual generation (Form EIA-923) summed and ranked | U.S. Energy Information Administration, U.S. Bureau of Reclamation United States | 2025 | In 2025 Vogtle (Georgia) produced 37.1 TWh and Palo Verde (Arizona) 31.3 TWh; all ten top plants by output were nuclear, running at 79-96% of capacity. Grand Coulee produced 16.2 TWh, 27th nationally, because hydro plants run well below full output for much of the year. | One year; Grand Coulee's output varies with river flow. Even at Reclamation's stated maximum of about 21 billion kWh it would remain well below the leading nuclear plants. | U.S. Energy Information Administration U.S. Energy Information Administration U.S. Bureau of Reclamation FactHub |
2. Drought pushed the share to its lows in 2023 and 2024, but not below half
The only two years below 60% were 2023 and 2024 (59.7% and 59.3%), when the Department of Ecology declared drought emergencies (12 watersheds in 2023; most of the state from April 16, 2024). EIA reported that 2023 monthly hydro output in Washington, Oregon, Idaho and Montana was near or below the low end of its 10-year range in most months. The share recovered to 63.6% in 2025.
Limit: Drought declarations describe water supply, not power output, and the declarations cover watersheds rather than the Columbia River system as a whole; the timing match is descriptive and does not by itself measure how much drought reduced generation.
Verify: State Historical Tables: Net Generation by State by Type of Producer by Energy Source, 1990-2025 (Final) Drought declaration news release, April 16, 2024 Drought conditions reduce hydropower generation, particularly in the Pacific Northwest (Today in Energy, November 7, 2024) Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
3. Measured by what utilities delivered to customers, hydro was just under half in 2024
Commerce's aggregate 2024 fuel mix for Washington utilities was 48.73% hydro, 15.44% unspecified, 13.33% natural gas, 9.6% wind, 5.91% coal and 5.13% nuclear. Hydro was by far the largest identified source, but in a drought year it was not a majority of what customers received.
Limit: One year only. 15.44% of delivered power was "unspecified" (mostly market purchases with no identified source), some of which may be hydro, so 48.73% is a floor rather than an estimate of the true hydro share. The figures are utility-reported resource claims, not metered physical flows, and were transcribed from Commerce's chart.
Verify: Fuel Mix Disclosure Washington electric utilities aggregate 2024 fuel mix (chart image) Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
4. Washington usually generates more than it sells, but imported on net in 2023 and 2024
In-state generation exceeded retail sales in every year from 2001 through 2024 (ratio 1.04 to 1.34); in 2024 in-state hydro alone equalled 67.5% of retail sales. EIA's estimate of net interstate trade shows Washington as a net exporter in most years (21-29 million MWh a year in 2020-2022) but a net importer in 2023 (1,170,693 MWh) and 2024 (385,768 MWh), as it also was in 2001 (10,176,675 MWh) and 2010 (1,279,785 MWh).
Limit: EIA computes net interstate trade as a residual that absorbs errors in estimated losses, and physical flows cannot show which plant served which customer. 2025 supply-and-disposition data are not yet published.
Verify: State Electricity Profiles: Washington, data tables (2024) State Historical Tables: Net Generation by State by Type of Producer by Energy Source, 1990-2025 (Final) Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
5. Washington is the largest hydropower-producing state
Washington ranked first among states for conventional hydro generation in every year 2001-2025, with 22.9% to 32.4% of the U.S. total. In 2025 it produced 64.7 TWh (26.8%), more than Oregon (28.7 TWh) and California (28.1 TWh) combined.
Limit: Credits each dam to the state where it stands; Columbia River output depends partly on water from Canada, Idaho and Montana.
Verify: State Historical Tables: Net Generation by State by Type of Producer by Energy Source, 1990-2025 (Final) Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
6. Grand Coulee has the most generating capacity of any U.S. power plant
Summing EIA-860 generators by plant, Grand Coulee has 6,809 MW of nameplate capacity (matching Reclamation's 6,809 MW) and 7,079 MW of net summer capacity, first on both measures. Vogtle (GA) is second on both, with 4,658 MW nameplate and 4,530 MW summer capacity. Excluding Grand Coulee's pump-generating units, its conventional hydro units alone total 6,495 MW.
Limit: Plant boundaries follow EIA plant codes. Capacity figures differ by definition: EIA-860 sums to 7,079 MW net summer capacity, while an EIA article cited about 6.7 GW; Reclamation operates the plant and is not independent of it.
Verify: Form EIA-860 Annual Electric Generator Report, 2025 final data Grand Coulee Dam: About Drought conditions reduce hydropower generation, particularly in the Pacific Northwest (Today in Energy, November 7, 2024) Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
7. By electricity produced, nuclear plants lead and Grand Coulee ranks 27th
In 2025 Vogtle (Georgia) produced 37.1 TWh and Palo Verde (Arizona) 31.3 TWh; all ten top plants by output were nuclear, running at 79-96% of capacity. Grand Coulee produced 16.2 TWh, 27th nationally, because hydro plants run well below full output for much of the year.
Limit: One year; Grand Coulee's output varies with river flow. Even at Reclamation's stated maximum of about 21 billion kWh it would remain well below the leading nuclear plants.
Verify: Form EIA-923 Power Plant Operations Report, 2025 final data Form EIA-860 Annual Electric Generator Report, 2025 final data Grand Coulee Dam: About Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
Common questions
“Washington imports power, so in-state generation says nothing about what Washington uses.”
Trade matters, which is why this check reports delivered power separately. But in most years Washington is a large net exporter, and in-state hydro alone equalled 67.5% of 2024 retail sales even in a drought year. The delivered fuel mix shows hydro as the largest source at 48.73% in 2024.
“Palo Verde is the largest U.S. power plant.”
By annual output Palo Verde is among the largest, but in 2025 Vogtle in Georgia, which has four operable reactors in EIA-860, produced more (37.1 vs 31.3 TWh). By capacity, Grand Coulee leads both: 6,809 MW nameplate versus 4,658 MW at Vogtle and 4,210 MW at Palo Verde.
“Grand Coulee's capacity is 6.7 GW, not 7 GW.”
Capacity has several definitions. Nameplate capacity sums to 6,809 MW, matching Reclamation. EIA-860's net summer capacity sums to 7,079 MW; an EIA article cited about 6.7 GW without saying which generating units it counted. All three figures rank Grand Coulee first; the next plant has about 4.5 GW of summer capacity.
“Hydro is declining, so the claim is out of date.”
The share has declined, from about 71% on average in 2001-2010 to 65.1% in 2016-2025, and it dipped below 60% in 2023 and 2024. It has not fallen below half of in-state generation in any year of the record.
“Unspecified power is really fossil fuel, so hydro is overstated.”
Unspecified power has no identified source by definition, so it cannot be assigned to hydro or to fossil fuels from these reports. This check treats the 48.73% hydro figure as a floor and does not claim hydro was a majority of 2024 delivered power.
Conclusion
Both halves of the claim hold under their most common meanings, and both need a qualifier. For generation, EIA's state data are unambiguous: hydro produced most of the electricity made in Washington in each of the last 25 years, never less than 59.3%, and Washington has been the nation's top hydro state every year, with roughly a quarter of U.S. hydro output. That is the strongest, best-documented part of the claim. The weaker part is the word "supplies." Washington trades heavily with neighboring states and Canada. In most years it generates far more than its customers buy; in-state hydro alone equalled 67.5% to 102.2% of retail sales from 2001 to 2024. But in the drought years 2023 and 2024 EIA estimates Washington was a small net importer, and Commerce's 2024 delivered fuel mix put hydro at 48.73%, a plurality but not a majority, with 15.44% of delivered power of unknown origin. Because some of that unspecified power may be hydro, the 2024 delivered share could be at or above half, but the data cannot show it. A careful version of the claim is that hydro generates most of Washington's electricity and is by far the largest source of the power its utilities deliver. For Grand Coulee, the answer depends on the measure. By installed capacity, nameplate or net summer, it is the largest U.S. plant by a wide margin, and EIA's generator census matches Reclamation's 6,809 MW figure exactly. By electricity produced in a year, it is not: nuclear plants such as Vogtle and Palo Verde run near full output all year and produced about twice as much or more in 2025. "Largest" in the claim is accurate if it refers to size, and wrong if it refers to output. The long-run trend is a slow decline in hydro's share as wind and natural gas grew, punctuated by drought. Nothing here establishes how much drought specifically reduced output, and the 2024 consumption-side figure is a single year. A wet 2025 brought the in-state share back to 63.6%.
How we checked
- Defined the claim as two statements: hydro supplies most of Washington's electricity, and Grand Coulee is the largest U.S. power plant, and separated generation from delivered power and capacity from annual output.
- Downloaded EIA's final state net generation tables (1990-2025), the Washington State Electricity Profile tables, and the 2025 final EIA-860 and EIA-923 files, and recorded each file's SHA-256.
- Computed hydro's share of Washington net generation for 2001-2025 and ranked all states by conventional hydro output each year.
- Summed EIA-860 generator capacity and EIA-923 net generation by plant code to rank U.S. plants by nameplate capacity, net summer capacity and 2025 output.
- Checked the EIA results against independent or operator sources: Commerce's 2024 delivered fuel mix, Reclamation's published capacity, and Ecology's drought declarations.
- Cross-checked EIA's two state tables (they agree within 4 MWh) and recorded every limit, including unspecified power, the residual trade estimate and differing capacity definitions.
- Published the tables, saved analyses and build scripts as a FactHub dataset so the numbers can be rerun.
Editorial note: Scope: this article checks two statements, hydro's share of Washington electricity and Grand Coulee's national rank. It does not evaluate hydropower's environmental effects, dam-removal debates or electricity prices. Data are EIA final data through 2025 (2024 for supply and disposition), Commerce's 2024 fuel mix and Reclamation's published plant description, as retrieved on October 9, 2026; EIA revises data, so later downloads may differ slightly. No external energy specialist review has been recorded. Independence note: the evidence comes from one country, four institutions (one federal statistical agency, one federal dam operator, two Washington State agencies), four methods (plant generation survey, generator capacity census, utility fuel-mix disclosure, drought declarations) and 2001-2025. Most figures rest on EIA survey data; the Commerce, Reclamation and Ecology sources are independent checks on parts of it. Reader verification checklist: 1. Click every source link and archived copy. 2. Check the limitation statements against the primary material. 3. Rerun the dataset's build scripts against the EIA files listed in its source manifest. 4. Submit counter-evidence via the challenge form. Challenge this fact-check: identify the specific conclusion you dispute and provide verifiable evidence that could change it. Credible challenges deserve review and a visible response.
Expert-review status
No external specialist review has been recorded. The data, scripts and limitations are published for direct reader verification.
Funding and conflicts
Funding: No external funding was received for this fact-check.
Ownership: FactHub is responsible for the article and its editorial process.
Conflicts: No known conflicts of interest are declared.
Sources
Sources are labeled by their role so readers can evaluate the evidence independently.
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Primary federal data: state generation by source
U.S. Energy Information Administration.
State Historical Tables: Net Generation by State by Type of Producer by Energy Source, 1990-2025 (Final)
Identifier: annual_generation_state.xlsx
EIA's annual state totals compiled from the Form EIA-923 plant survey. Source of every hydro-share and state-ranking figure. Chosen because it is the official, complete national series for all states and years.
Archived copy captured October 9, 2026 -
Primary federal data: supply, sales and trade
U.S. Energy Information Administration.
State Electricity Profiles: Washington, data tables (2024)
Identifier: SEP Tables for WA.xlsx, Table 10
Table 10 gives Washington retail sales, international trade and EIA's estimate of net interstate trade, which separate in-state generation from in-state use.
Archived copy captured October 9, 2026 -
Primary federal data: generator capacity census
U.S. Energy Information Administration.
Form EIA-860 Annual Electric Generator Report, 2025 final data
Identifier: eia8602025.zip, 3_1_Generator_Y2025.xlsx
Nameplate and net summer capacity of every operable U.S. generator at the end of 2025; summed by plant to rank plants by capacity.
Archived copy captured October 9, 2026 -
Primary federal data: plant-level generation
U.S. Energy Information Administration.
Form EIA-923 Power Plant Operations Report, 2025 final data
Identifier: f923_2025.zip, Schedules 2-5 Page 1
Net generation of every U.S. plant in 2025; summed by plant to rank plants by annual output.
Archived copy captured October 9, 2026 -
State compilation: electricity delivered to customers
Washington State Department of Commerce.
Fuel Mix Disclosure
Commerce compiles the resources more than 60 Washington utilities and BPA report using to serve Washington customers. Chosen as an independent, consumption-side check on the EIA generation figures.
Archived copy captured October 9, 2026 -
State data: 2024 delivered fuel mix
Washington State Department of Commerce.
Washington electric utilities aggregate 2024 fuel mix (chart image)
The labeled chart from which the 2024 percentages were transcribed.
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Operator statement
U.S. Bureau of Reclamation.
Grand Coulee Dam: About
The dam's owner and operator gives its generating capacity (6,809 MW) and typical output (up to 21 billion kWh a year). Chosen as a check on EIA capacity figures from the institution that runs the plant.
Archived copy captured October 9, 2026 -
Federal analysis: drought and hydro
U.S. Energy Information Administration.
Drought conditions reduce hydropower generation, particularly in the Pacific Northwest (Today in Energy, November 7, 2024)
Explains the 2023-2024 low-water years in the Columbia River Basin and gives Grand Coulee's net summer capacity as 6.7 GW.
Archived copy captured October 9, 2026 -
State hydrologic declaration
Washington State Department of Ecology.
Drought declaration news release, April 16, 2024
Dates the 2024 statewide drought emergency and the 2023 emergency covering 12 watersheds; independent of the electricity data.
Archived copy captured October 9, 2026 -
Curated data, saved analyses and reproduction scripts
FactHub.
Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
Identifier: dataset:wa-electricity-generation-by-source:1
Every number in this article, with the tables, field definitions, source digests, build scripts and limitations needed to reproduce it.
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Chart of the hydro share
FactHub.
Hydropower's share of electricity generated in Washington, 2001-2025
Identifier: chart:wa-hydro-share-of-generation:2
Chart of the wa-hydro-share-annual saved analysis.
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FactHub dataset
Washington Electricity Generation by Source and the Largest U.S. Power Plants, 2001-2025
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Tables: wa-hydro-annual, wa-generation-by-source
Saved analysis wa-hydro-share-annual; table wa-hydro-annual
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Tables: wa-hydro-annual
Saved analysis wa-hydro-share-summary
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Tables: wa-hydro-annual, state-hydro-rank-2025
Saved analyses wa-hydro-state-rank and state-hydro-top10-2025
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Tables: wa-supply-disposition
Saved analysis wa-generation-vs-retail-sales; table wa-supply-disposition
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Tables: wa-utility-fuel-mix-2024
Saved analysis wa-utility-fuel-mix-2024
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Tables: largest-plants-capacity-2025
Saved analysis largest-plants-by-capacity-2025
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Tables: largest-plants-generation-2025
Saved analysis largest-plants-by-generation-2025
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Tables: largest-plants-capacity-2025, largest-plants-generation-2025
Saved analysis grand-coulee-2025-summary and its replications
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- FactHub chart wa-hydro-share-of-generation
Update history
- Initial version.
- Rating standardized under FactHub's verdict rules (was "Mostly true"); the headline now states the finding. The evidence and conclusion are unchanged.
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