During World War II, Tacoma had to buy power from the Bonneville Power Administration and from Seattle, which cost $1 million each year. Until that time, hydroelectric dams were viewed in the Northwest almost as a patriotic act and power shortages after the war demonstrated the pressing need for more. Tacoma built two dams during the war and added generators to existing hydro and steam facilities. Even before the war ended, Tacoma City Light started looking for new sites for hydropower. The Cowlitz River in Lewis County was selected and the City announced its plans in 1948. Construction was to have taken “three or four years” (Malloy, 172).
Opposition rose immediately from sportsmen’s groups and the State Game Department. A state legislator introduced legislation authorizing the department to dynamite Tacoma’s Cushman dams because they lacked fish ladders (the measure died). The legislature did establish a fish sanctuary on the Cowlitz that blocked the project. Tacoma went to court and the matter went to the U.S. Supreme Court three times before the city prevailed.
Construction on Mayfield began on July 7, 1955. It was to be 850 feet long and 185 feet high and would generate 460,000 kilowatts. An 860-foot tunnel connected the reservoir and the powerhouse. In 1957, the project stopped due to court action, but was restarted in 1959. Total cost of the dam was $44.5 million.
The dam included a $4.5 million system that carried adult fish from the river up and over the dam to the lake. In 1967, City Light finalized $20 million in plans for two hatcheries to maintain the salmon and steelhead runs in the river.
Mossyrock Dam, 13 miles upstream, was completed in 1968.