Mayfield — Plant Summary
- EIA Plant ID
- 3917
- Capacity
- 162 MW
- Primary Fuel
- Hydro
- Technology
- Conventional Hydroelectric
- Status
- Operating
- Location
- Lewis, WA
- Operating Since
- 1963
- Generators
- 4
- Operator
- City of Tacoma - (WA)
- Parent Company
- —
- Annual Generation
- 576,354 MWh
- Capacity Factor
- 40.6%
- Balancing Authority
- City of Tacoma, Department of Public Utilities, Light Division
- ISO/RTO
- —
- NERC Region
- WECC
Mayfield
OperatingHydro
Ranked #18 of 75 Hydro plants in WA#120 of 1454 nationally
162 MW Hydro operating in Lewis, WA — City of Tacoma, Department of Public Utilities, Light Division
EIAGEMWD
162 MW
Nameplate Capacity
4
Generators
units
Conventional Hydroelectric
Technology
1963
Operating Since
Location
Coordinates
46.5035, -122.5885
County
Lewis, WA
Nearby Plants
- MossyrockHydro300 MW · 13.0 km
- Skookumchuck Wind FacilityWind136 MW · 23.4 km
- Chehalis Generating FacilityNatural Gas593.3 MW · 28.1 km
Ownership & Operator
Owner data does not fully agree across sources.
EIA typically reports the operating utility, while GEM resolves to the financial owner or parent corporation. Both can be correct.
| Field | EIA | GEM | Wikidata |
|---|---|---|---|
| Operator | City of Tacoma - (WA) | Tacoma Power | — |
| Owner(s) | City of Tacoma - (WA) | Tacoma Power [100%] | — |
| Status | Operating | operating | — |
Ownership Chain
GEM identifies the owner as Tacoma Power [100%]
This entity is not yet in the GEM ownership database — chain unavailable.
About
The Mayfield hydroelectric plant, located in Lewis County, Washington, has a total capacity of 162 MW across four generators. The plant began operating in 1963 and is owned and operated by the City of Tacoma. It utilizes conventional hydroelectric technology with water as its primary fuel source (WAT). Mayfield is ranked as the 18th largest power plant in Washington state out of 23, and 120th nationally out of 194.
In the most recent year with available data, Mayfield generated 576,354 MWh of electricity, resulting in a capacity factor of 40.6%. The plant operates within the Western Electricity Coordinating Council (WECC) NERC region, and the balancing authority is the City of Tacoma, Department of Public Utilities, Light Division.
Generated from EIA, GEM, and public data sources
Engineering & Generators
Grid Context
NERC Region
WECC
Balancing Authority
City of Tacoma, Department of Public Utilities, Light Division
Grid Voltage
240 kV
Regulatory Status
RE
Entity Type
Municipal
Sector
Electric Utility
Generation
56.9K MWh
Latest Month
576.4K MWh
Annual Generation
40.6%
Capacity Factor
Jan 2022 – Dec 2024
Financial Data
No financial data available for this plant.
Pricing & Market Data
This plant is outside organized wholesale electricity markets (ISOs/RTOs). Nodal pricing data is not available.
News & Articles (10)Beta
General
Keeping Washington’s power flowing: Why dam maintenance matters
In Washington state, hydropower is the most affordable and reliable supplier of clean energy.
The Seattle Times·2 months ago
General
Keeping Washington’s power flowing: Why dam maintenance matters
In Washington state, hydropower is the most affordable and reliable supplier of clean energy.
The Seattle Times·2 months ago
General
Keeping Washington’s power flowing: Why dam maintenance matters
In Washington state, hydropower is the most affordable and reliable supplier of clean energy.
The Seattle Times·2 months ago
General
Keeping Washington’s power flowing: Why dam maintenance matters
In Washington state, hydropower is the most affordable and reliable supplier of clean energy.
The Seattle Times·2 months ago
Last updated 2026-03-26
View all 10 articles