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Mayfield Dam

Mayfield Dam serves nearly 58,000 homes each year

Mayfield Dam, completed in 1963, includes a 250-foot-high (above bedrock), 850-foot-long, concrete arch and gravity dam that forms Mayfield Lake.

In addition to the Cowlitz River, water from the Tilton River also contributes to Mayfield Lake. An 854-foot-long power tunnel passes through the right abutment of the dam and terminates at a concrete forebay structure. Four penstocks continue from the forebay structure to the four 40,500 kilowatt vertical Francis turbines for an installed capacity of 162 megawatts.

Mayfield Lake

Make a splash at Mayfield Lake

The 2,250-acre lake is formed by the Mayfield Dam and offers year-round recreation. The elevation of the lake fluctuates no more than 10 feet throughout the year. Public boat ramps and campgrounds are located at Mayfield Lake Park and Ike Kinswa State Park, which is mostly located on Tacoma Power property. Several privately run recreational areas operate with permits from Tacoma Power.

Tacoma Power owns the shoreline around Mayfield Lake, some of which is designated for wildlife habitat. Under certain situations, permits are issued to neighboring property owners who wish to have a boat dock on the lake and meet the conditions of the permit.


  • Year completed - 1963
  • River system - Cowlitz
  • Original investment - $44.5 million
  • Type of dam - concrete arch/gravity and embankment
  • Height - above riverbed, 200 feet; above bedrock, 250 feet
  • Length - 850 feet
  • Width - top, 5 feet; base, 23 feet
  • Volume of concrete in dam - 110,000 cubic yards
  • Average flow - 6,120 cubic feet/second
  • Drainage area - 1,400 square miles
  • Reservoir length - 13 miles
  • Miles of shoreline - 33.5 miles
  • Reservoir area at maximum elevation - 2,250 acres
  • Reservoir elevation - full, 425 feet; lowest allowable, 415 feet
  • Average annual generation - 804 million kilowatt-hours
  • Equivalent number of NW homes served - 57,500
  • Number of generators - Four 40,500 kilowatt generators 
  • Installed capacity (nameplate rating) - 162,000 kilowatts