Ruth Reservoir is the only reservoir on California's Mad River. The reservoir and adjacent community were named for early settler Ruth McKnight. The reservoir was formed by construction of R. W. Matthews Dam in 1962 primarily for domestic and industrial water supply to Arcata, Eureka, and other communities around Humboldt Bay. The reservoir was not designed for flood control storage, but nonetheless limited December 1964 flooding to 51 percent of 1955 flow through the community of Mad River and 90 percent of the 1955 flood flow at Arcata. A 2-MW hydro-electric plant with two 1-MW turbine generators is powered by water released from the reservoir. The plant generates 5 GWh during an average water year. Dry-weather releases flow down the Mad River from the reservoir to be recovered by Humboldt Bay Municipal Water District's Ranney collectors near Essex, California.