The Portland District, U.S. Army Corps of Engineers (USACE), completed the final Supplemental Environmental Impact Statement (SEIS) for the continued operation and maintenance of the Willamette Valley System and published it on May 22, 2026. We issued a Record of Decision for the Final SEIS on June 23, 2026, outlining how we addressed the new Endangered Species Act (ESA) obligations and how we will operate the Willamette Valley System of dams. Following this ROD, we are immediately reconsulting with the National Marine Fisheries Service (NMFS) and continuing discussions with the U.S. Fish and Wildlife Service (USFWS) to find long-term, practical actions that will support endangered fish and come with a lower price tag.

Current funding limitations and design requirements have prompted the need to explore alternative, cost-effective solutions. We will focus on immediate, “operational” measures – such as changing how and when water is released from the dams. Continuing the operations, termed “Interim Operations” in the SEIS, allows the action agencies, USACE, Bonneville Power Administration, and the U.S. Bureau of Reclamation, to meaningfully consult while ensuring conditions for listed species continue to improve.

We are implementing the Interim Operations across the Willamette Valley.

• Green Peter:  Deep fall drawdown and spring spill to guide downstream migration.
• Lookout Point:  Deep late-fall drawdown and spring spillway usage to provide volitional passage.
• Cougar:  Deep late-fall drawdown followed by a delayed spring reservoir refill.
• Foster:  Delayed spring refill and use a specialized summer attraction-flow fish weir.
• Hills Creek:  Prioritized nighttime winter water releases to align with natural wild fish migration.
• Big Cliff:  Spill spreading across multiple bays to reduce total dissolved gas levels and improve downstream water quality.
• Detroit:  A phased, deep fall drawdown for safe salmon passage, actively managed to protect downstream water quality and ensure a reliable summer refill.

Background
 The EIS and SEIS provide us and the public with a comprehensive understanding of how our operations may affect the environment, communities, and surrounding ecosystems. Shortly before the final Willamette Valley System Operations and Maintenance Final Environmental Impact Statement was published on May 16, 2025, two significant developments introduced new issues for consideration, prompting the need for a SEIS to evaluate the effects. We issued a ROD for the EIS on May 13, 2025 while we drafted the SEIS.

USACE prepared the final SEIS to analyze the deeper fall drawdown at Detroit Reservoir to improve juvenile fish passage from the 2024 NMFS Biological Opinion and stopping hydropower generation at the projects, as requested by Congress in the Water Resources Development Act (WRDA) of 2024. 

1. Implementing a deeper fall drawdown of Detroit Reservoir

In late December 2024 NMFS published a Biological Opinion with a Reasonable and Prudent Alternative that directed USACE to implement a deeper fall drawdown at Detroit Reservoir to support the protection of endangered fish species.

We are taking a careful, "step down" approach to the Detroit drawdown to reduce turbidity that would impact local water systems and downstream river health:

• Incremental approach: In the first year, we will lower the reservoir to 1,425 feet – a level reached safely in past without causing muddy water (turbidity) issues downstream. In following years, we will lower the reservoir to 1395 feet – the target for safe fish passage through the regulating outlet.
   
• Real-time management: We will monitor water quality in real-time. If measurements show that turbid water is moving downstream and is likely to impact local drinking water systems, we will pause, modify, or stop the drawdown.

2. Studying a permanent end to hydropower production at Willamette Valley dams
 In January 2025, the President signed WRDA 2024 into law, which directed USACE to look at a new option, or alternative, which stops federal hydropower operations at Willamette Valley dams. The review found that completely shutting down the dam's hydropower function would require multi-million-dollar retrofits to the dams to safely bypass water and inspect the dams. Retrofits to the outlets to slow the water falling through the dam would still injure species even if turbines are removed. SEIS showed that shutting down hydropower generation would provide no extra benefit to migrating fish without additional major changes to operations that would impact water supply.