Washington Utilities and Transportation Commission
The Department of Ecology provides lists of dam types and locations for the most of the dams in the state.
See their report: Inventory of Dams Report
Most dams are privately owned, built for recreation or irrigation, and of earthen construction. Less than 7 percent of dams in Washington were constructed for the purpose of generating hydroelectricity. Washington has 1,125 dams; of those 380 of are located in six counties: King, Pierce, Lewis, Grant, Yakima and Chelan. All other counties each have less than 4 percent of the total number of dams in the state.