# Lower Monumental

BPA asset profile · https://askthegrid.com/assets/facilities/lower-monumental

U.S. Army Corps of Engineers, Walla Walla District - Walla Walla County - BPAT

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.

## Metrics

- **Nameplate capacity:** 675 MW — Canonical EIA plant baseline.
- **Registry anchor:** Plant 3927 — plant-3927

## Facts

- **Technology:** Conventional Hydroelectric
- **Operator:** U.S. Army Corps of Engineers, Walla Walla District

## Related parties

- **Owner / operator:** U.S. Army Corps of Engineers, Walla Walla District — Owner ([source](https://www.nww.usace.army.mil/))
- **Power marketer / balancing authority:** Bonneville Power Administration — BPAT balancing authority and wholesale power marketer ([source](https://www.bpa.gov/))
- **O&M provider / equipment supplier:** ANDRITZ HYDRO — Equipment supplier (original generators and three turbines) and rehabilitation contractor ([source](https://www.andritz.com/hydro-en/hydronews/hydro-news-29/hy-hn29-11-usa-lower-monumental-dam))

## Sources

- [historylink.org](https://historylink.org/File/8022) — historylink.org · public_source — Source retained for exact-record publication review.
- [andritz.com](https://www.andritz.com/hydro-en/hydronews/hydro-news-29/hy-hn29-11-usa-lower-monumental-dam) — andritz.com · public_source — Source retained for exact-record publication review.
- [bpa.gov](https://www.bpa.gov/energy-and-services/power/hydropower-impact) — bpa.gov · authoritative — Source retained for exact-record publication review.
- [federalregister.gov](https://www.federalregister.gov/documents/2009/06/19/E9-14448/central-ferry-lower-monumental-transmission-line-project) — federalregister.gov · authoritative — Source retained for exact-record publication review.

---

Canonical page: https://askthegrid.com/assets/facilities/lower-monumental
Website: [U.S. federal government (U.S. Army Corps of Engineers)](https://www.nww.usace.army.mil/)

Source: Ask the Grid — https://askthegrid.com/