title: "Hydroelectric Power in America" description: How dams and water generate electricity — the history, technology, economics, and environmental trade-offs of America's oldest renewable energy source. summary: How dams and water generate electricity — the history, technology, economics, and environmental trade-offs of America's oldest renewable energy source. category: hydro difficulty: Intermediate updated: 2026-02-10 tags: ["hydro", "hydroelectric", "dam", "renewable energy", "pumped storage", "water power"] relatedTools: [] faqs:
- question: How much of U.S. electricity comes from hydropower? answer: Hydropower generates about 6% of U.S. electricity (roughly 260 TWh/year), making it the largest single source of renewable electricity after wind. It provides about 28% of all renewable generation. Capacity fluctuates year to year depending on precipitation and snowpack levels.
- question: Are new dams being built in the U.S.? answer: Very few new large dams are being built because most suitable sites are already developed and environmental concerns make permitting extremely difficult. Growth is coming from upgrading existing facilities, adding generation to non-powered dams (only about 3% of U.S. dams generate electricity), and expanding pumped storage capacity.
- question: Is hydropower truly renewable? answer: Hydropower is renewable in the sense that it relies on the water cycle (rainfall and snowmelt replenish reservoirs). However, climate change is altering precipitation patterns, and prolonged droughts can significantly reduce output — as seen in the western U.S. in recent years. Reservoirs also have finite lifespans due to sedimentation.
- question: What is pumped storage hydropower? answer: Pumped storage uses two reservoirs at different elevations. When electricity is cheap or abundant (e.g., midday solar), water is pumped uphill. When electricity is needed, water flows back downhill through turbines. It's the largest form of grid-scale energy storage in the world, with about 22 GW of capacity in the U.S.
Hydroelectric Power in America
Hydropower was America's first significant source of renewable electricity — and it still provides more clean, dispatchable power than any other single renewable source. Understanding its capabilities, limitations, and future role is essential to understanding the U.S. energy system.
How Hydroelectric Power Works
Conventional (Impoundment) Dams
The most common type. A dam creates a reservoir, storing potential energy. Water released from the reservoir flows through turbines connected to generators.
Key components:
- Dam: Holds back water, creating a head (height difference)
- Intake: Controls water flow into the penstock
- Penstock: Pipe or channel carrying water to the turbine
- Turbine: Converts water's kinetic energy to rotational energy (Francis, Kaplan, or Pelton types depending on head and flow)
- Generator: Converts rotational energy to electricity
- Spillway: Releases excess water safely during floods
Power output depends on two factors:
- Head: The vertical distance water falls (higher = more energy)
- Flow: The volume of water per second (more flow = more energy)
Run-of-River
No significant reservoir. Generators use the natural flow of the river. Output varies with river conditions — less controllable than impoundment dams but lower environmental impact.
Pumped Storage Hydropower (PSH)
Two reservoirs at different elevations connected by a tunnel/penstock:
- Charging: Pumps move water from lower to upper reservoir (consuming electricity)
- Discharging: Water flows downhill through turbines (generating electricity)
- Round-trip efficiency: 70-85%
- Storage duration: Hours to days (limited by reservoir volume)
U.S. Hydropower by the Numbers
| Metric | Value | |--------|:-----:| | Total conventional capacity | ~80 GW | | Pumped storage capacity | ~22 GW | | Annual generation | ~260 TWh (varies with precipitation) | | Share of U.S. electricity | ~6% | | Share of U.S. renewable electricity | ~28% | | Number of hydropower plants | ~2,200 | | Number of U.S. dams | ~91,000 | | Dams with power generation | ~2,500 (less than 3%) |
Top Hydropower States
| State | Capacity (GW) | Share of State Electricity | |-------|:-:|:-:| | Washington | 21.6 | ~65% | | Oregon | 8.5 | ~40% | | California | 14.1 | ~10-15% (varies with drought) | | New York | 5.8 | ~20% | | Alabama | 3.4 | ~6% | | Tennessee | 3.3 | ~10% | | Montana | 2.8 | ~35% | | Idaho | 2.6 | ~50% |
The Pacific Northwest dominates due to the Columbia River system. The Grand Coulee Dam in Washington (6.8 GW) is the largest U.S. power plant of any type.
Major U.S. Hydropower Facilities
| Dam | State | Capacity (MW) | River | |-----|-------|:-:|---------| | Grand Coulee | WA | 6,809 | Columbia | | Bath County PSH | VA | 3,003 | Back Creek | | Chief Joseph | WA | 2,620 | Columbia | | Robert Moses Niagara | NY | 2,525 | Niagara | | John Day | OR/WA | 2,160 | Columbia | | Hoover | NV/AZ | 2,080 | Colorado | | The Dalles | OR/WA | 1,807 | Columbia | | Glen Canyon | AZ | 1,320 | Colorado |
Economics
Levelized Cost of Energy
Hydropower has some of the lowest operating costs of any electricity source:
| Type | LCOE ($/MWh) | |------|:-:| | Existing hydropower (operating) | $10-$30 | | Upgraded existing facility | $30-$60 | | New run-of-river | $40-$80 | | New pumped storage | $50-$100 | | New impoundment dam | $50-$150+ |
Existing hydropower is among the cheapest electricity available — the dams are paid off, and water is free. New large dams are expensive due to construction costs and environmental mitigation.
Revenue Streams
Hydropower earns money from multiple sources:
- Energy: Selling electricity (often under long-term contracts)
- Capacity: Being available to generate on demand (dispatchable)
- Ancillary services: Frequency regulation, spinning reserves, voltage support
- Flood control: Many federal dams serve flood management roles
- Renewable energy credits (RECs): In states that count hydro as renewable
Environmental Considerations
Benefits
- Zero direct emissions: No fuel combustion, no CO2, no air pollution during operation
- Dispatchable: Can ramp up and down quickly to balance the grid
- Long-lived: Dams can operate 50-100+ years
- Multi-use: Recreation, flood control, water supply, irrigation, navigation
Concerns
- Fish passage: Dams block salmon and other migratory fish. The Columbia River system has seen salmon populations decline dramatically. Fish ladders help but don't fully solve the problem.
- Ecosystem disruption: Reservoirs flood valleys, alter downstream water temperature/flow, and trap sediment
- Methane emissions: Reservoirs in warm climates can emit methane from decomposing vegetation (though emissions per kWh are far below fossil fuels)
- Displacement: Dam construction has historically displaced communities, particularly Indigenous peoples
- Climate vulnerability: Droughts reduce output. Lake Mead (Hoover Dam) and Lake Powell (Glen Canyon) have dropped to historically low levels during western droughts
Dam Removal Movement
A growing trend in the U.S.:
- Over 2,000 dams removed since the 1990s
- Most are small, obsolete, or no longer serving their original purpose
- Klamath River (OR/CA): Four dams removed in 2023-2024 — the largest dam removal in U.S. history, restoring 400 miles of salmon habitat
- Elwha River (WA): Two dams removed (2011-2014); salmon returned within months
- Balancing act: restoration benefits vs. losing clean generation capacity
Future of U.S. Hydropower
Growth Opportunities
- Powering non-powered dams: Adding generation to existing dams that currently don't produce electricity. DOE estimates 12 GW of potential from this approach alone.
- Efficiency upgrades: Modernizing turbines at existing plants can increase output 5-15% without any new construction.
- New pumped storage: Critical for grid storage. FERC has issued preliminary permits for dozens of new PSH projects totaling 60+ GW, though most will not be built.
- Conduit hydropower: Small turbines in irrigation canals, water treatment outflows, and pipelines.
Challenges
- Relicensing: Many FERC licenses (issued for 30-50 years) are coming up for renewal, with stricter environmental requirements
- Climate change: Shifting precipitation patterns and reduced snowpack threaten western hydropower reliability
- Sedimentation: Reservoirs gradually fill with sediment, reducing storage capacity (a very long-term issue)
- Competition for water: Agriculture, municipal supply, environmental flows, recreation — hydropower is one of many demands
Pumped Storage Renaissance
Pumped storage is experiencing renewed interest as the grid needs more storage:
- Currently 43 proposed projects before FERC
- "Closed-loop" designs (not connected to natural waterways) reduce environmental impact
- Some proposals repurpose abandoned mines or quarries
- Can provide 8-12+ hours of storage — far longer than most battery installations
Hydropower's Grid Value
What makes hydropower uniquely valuable:
- Dispatchable: Unlike wind and solar, hydro can generate on demand within seconds
- Black start capable: Can restart the grid after a blackout (no external power needed)
- Load following: Adjusts output to match demand throughout the day
- Grid stability: Massive rotating generators provide inertia that stabilizes grid frequency
- Storage: Pumped hydro provides the only commercially proven long-duration grid storage at scale
As wind and solar grow, hydropower's flexibility becomes more valuable — ramping up when the sun sets or the wind dies, and backing down when renewables are abundant.