Mossyrock — Plant Summary
- EIA Plant ID
- 3918
- Capacity
- 300 MW
- Primary Fuel
- Hydro
- Technology
- Conventional Hydroelectric
- Status
- Operating
- Location
- Lewis, WA
- Operating Since
- 1968
- Generators
- 2
- Operator
- City of Tacoma - (WA)
- Parent Company
- —
- Annual Generation
- 902,717 MWh
- Capacity Factor
- 34.3%
- Balancing Authority
- City of Tacoma, Department of Public Utilities, Light Division
- ISO/RTO
- —
- NERC Region
- WECC
Mossyrock
OperatingHydro
Ranked #14 of 75 Hydro plants in WA#70 of 1454 nationally
300 MW Hydro operating in Lewis, WA — City of Tacoma, Department of Public Utilities, Light Division
EIAGEMWD
300 MW
Nameplate Capacity
2
Generators
units
Conventional Hydroelectric
Technology
1968
Operating Since
Location
Coordinates
46.5347, -122.4247
County
Lewis, WA
Nearby Plants
- MayfieldHydro162 MW · 13.0 km
- Skookumchuck Wind FacilityWind136 MW · 23.2 km
- Cowlitz FallsHydro70 MW · 25.3 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
Mossyrock Dam is a concrete double-arch-gravity dam on the Cowlitz River near Mossyrock in Lewis County, Washington, United States. The reservoir created by the dam is called Riffe Lake. The primary purpose of the dam is hydroelectric production while flood control is a secondary function. The dam is the tallest in Washington state and its hydroelectric power station supplies 40% of Tacoma Power's electricity.
Read more on WikipediaMossyrock is a 300 MW hydroelectric power plant located in Lewis County, Washington. The plant began operating in 1968 and is owned and operated by the City of Tacoma - (WA). It utilizes conventional hydroelectric technology with water as its primary fuel source. The facility consists of 2 generators. Mossyrock is the 14th largest power plant in Washington out of 23, and ranks 71st nationally out of 194 plants.
In the most recent year of data, Mossyrock generated 902,717 MWh of electricity, achieving a capacity factor of 34.3%. The plant operates within the Western Electricity Coordinating Council (WECC) NERC region, and its 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
185.2K MWh
Latest Month
902.7K MWh
Annual Generation
34.3%
Capacity Factor
Jan 2023 – Dec 2025
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 (8)Beta
General
The Story Behind The Riffe Lake Underwater Town In Washington
Thanks to a lengthy logging and coal mining history, there are a fair amount of ghost towns in Washington. Most of them have been diminished to nothing,...
Only In Your State·6 months ago
Industry·corporate
Commissioner Brummer and Congresswoman tour Lewis County natural resources
From left, U.S. Congresswoman Marie Gluesenkamp-Perez, Lewis County Commissioner Scott Brummer and Chris Mattson, Power Generation Manager...
Marie Gluesenkamp-Perez (other)Scott Brummer (other)
Lewis County Washington (.gov)·2 years ago
General
Scholarship keeps Mossyrock kids on course for college
Kindergartners don't typically think about college or paying for it. Neither do sixth graders, for that matter.
king5.com·8 years ago
Hazards·earthquake
Tacoma Power to reduce water level at Riffe Lake due to quake concerns for Mossyrock Dam
Updated earthquake concerns for Mossyrock Dam, the tallest structure of its kind in Washington, have prompted Tacoma Power to commit to a new, reduced water...
Tacoma Power (operator)Mossyrock Dam (other)
FOX 13 Seattle·9 years ago
Last updated 2026-03-14
View all 8 articles