The U.S. Army Corps of Engineers, Portland District (Corps) announces the availability of the Final Supplemental Environmental Impact Statement (Final SEIS) for the Willamette Valley System Operations. A formal Notice of Availability was published in the Federal Register on May 22, 2026.
The Final SEIS evaluates the potential environmental, economic, and social impacts associated with the continued operation and maintenance of the 13 federal dams and reservoirs within the Willamette Valley System. This supplemental document was prepared to address new legislative and regulatory requirements that emerged late in the development of the original Environmental Impact Statement.
Specifically, the Final SEIS evaluates two new primary requirements:
Hydropower Authorization: An alternative that removes hydropower as an authorized function at certain Willamette Valley dams, as directed by the Water Resources Development Act (WRDA) of 2024.
Detroit Reservoir Drawdown: The effects of implementing a deeper fall drawdown at Detroit Reservoir to support the protection of endangered fish species, as directed by a National Marine Fisheries Service Biological Opinion.
The document analyzes these proposed operational modifications, which are designed to comply with the Endangered Species Act for threatened Upper Willamette River Chinook salmon and winter steelhead, while continuing to evaluate impacts to other congressionally authorized purposes, such as flood risk management.
The publication of the Final SEIS is a required environmental compliance milestone but is not a final agency decision. Following the conclusion of the 30-day regulatory review period for the Final SEIS, the Corps will issue a final decision. This decision will be documented and published in a Record of Decision (ROD), which is anticipated in June.
The Final SEIS, along with all associated appendices, is available for public review and download at the following locations:
Environmental Protection Agency website https://cdxapps.epa.gov/cdx-enepa-II/public/action/eis/details?eisId=559841
Portland District website at https://www.nwp.usace.army.mil/WVS-EIS/
Questions or requests for information regarding the Final SEIS may be directed to:
Liz Oliver, Project Manager
U.S. Army Corps of Engineers, Portland District
Email: liz.oliver@usace.army.mil
Phone: 503-808-4712