Lower Monumental

U.S. federal government (U.S. Army Corps of Engineers)Walla Walla CountyBPAT

Lower Monumental Dam is a conventional hydroelectric plant on the Snake River in Walla Walla County, Washington, with five operating turbine-generators totaling 675 MW of nameplate capacity. It is owned and operated by the U.S. Army Corps of Engineers, whose Walla Walla District runs the facility as one of the four Lower Snake River dams built under the 1945 Lower Snake River Project. The plant's power is marketed into the Bonneville Power Administration balancing area, with settlement occurring at generator nodes located at the plant site. All five units remain in commercial operation with no retirement date scheduled in federal filings. Lower Monumental is nonetheless at the center of a long-running Endangered Species Act lawsuit over salmon impacts; a 2023 federal-tribal-state agreement paused that litigation, with a court-approved stay running through December 13, 2028, while the dam continues to operate. Any actual breaching of the dam would require an act of Congress, which has not occurred.