Mayfield

Hydro power plant · Lewis County, Washington

Nameplate capacity
162 MW
Rank in Washington
#39
of 139 plants
In service since
1963
March 1963

Details

Primary fuel
Hydro
Technology
Conventional Hydroelectric
Operator
City of Tacoma - (WA)
County
Lewis County
Generating units
4
Share of state capacity
0.51%
Rank among hydro plants in Washington
#18 of 73
EIA plant code
3917

Generating units

Individual generating units at Mayfield
UnitTechnologyNameplateSummerOnlineStatus
41Conventional Hydroelectric41 MW41 MW1983Operating
42Conventional Hydroelectric41 MW41 MW1963Operating
43Conventional Hydroelectric41 MW41 MW1963Operating
44Conventional Hydroelectric41 MW41 MW1963Operating

Nameplate is the maximum rated output; summer capacity is what the unit can reliably deliver on a hot day, which is typically lower.

Similarly sized plants in Washington

EncogenNatural gas176 MW
WhitehornNatural gas169 MW
Hopkins Ridge WindWind157 MW
Juniper Canyon I Wind ProjectWind151 MW

About this data

From EIA’s inventory of operable generators, May 2026 release. Capacity is nameplate — the maximum rated output of the equipment, not what the plant actually generates over a year, which depends on how often it runs. A 162 MW solar plant and a 162 MW nuclear plant have the same entry here and produce very different amounts of electricity.

“In service since” is the earliest in-service date among the units still listed, so a site rebuilt around newer equipment can read as younger than the site itself. All Washington power plants · What Washington actually generates