[4] Planning for the Mossyrock Dam began in the 1940s but opposition from local fishers and Washington State's Fish and Wildlife Department delayed construction.

During World War II, the city of Tacoma, Washington, purchased its electricity from the Bonneville Power Administration and from Seattle, with costs of up to $1 million/year.

The Washington State Legislature enacted a fish sanctuary on the Cowlitz River that initially blocked the project.

Eventually moved to the area which was flooded due to the dam, it was renamed in honor of Floyd Riffe approximately in 1897.

The power plant upgrade increased the total capacity by 70 MW, with an expected overall energy conversion efficiency of near 95 percent.