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Ecology's work near you > River basins & groundwater > Lower Snake River

Lower Snake River Water Replacement Study

The Washington state legislature directed us to evaluate the impacts of changing water management on the Lower Snake River because understanding how water is being used and allocated in the region is essential to preserving both the state’s natural resources and its multi-billion-dollar agricultural economy.

About the study

The Lower Snake River Water Replacement Study provides a comprehensive analysis of water use for irrigation, municipal, and industrial purposes under the potential scenario of lower Snake River dam breaching. This study is one of four studies originally initiated by federal agencies to better understand potential impacts of a dam breach. The other studies focused on impacts and adaptation options related to transportation, energy reliability, and recreation. None of these studies were intended as decision documents, but they would likely inform future analysis and decisions.

The study details current water supply and uses near the four lower Snake River dams (Ice Harbor, Lower Monumental, Little Goose, Lower Granite) in Washington and Idaho and evaluates impacts to water delivery and mitigation approaches in the event they were breached. The study analyzes approaches for providing replacement for irrigation, municipaI, and industrial water supplies and services currently provided by the lower Snake River dams. The evaluation includes each dam individually and all four dams as a system.

The Study included significant Tribal and stakeholder outreach and engagement to collect data and information from those whose water supply could be most affected if the dams were to be breached. Technical analyses covered the following:

  • Documentation about the current water supply resulting from the Lower Snake River dams
  • Availability of water, now and into the future, with and without the dams in place
  • Potential solutions, or adaptations, to provide water supply to current water users if the dams were breached
  • Identification and analysis of potential implementation issues related to adapting water supplies in a dam breach scenario

Timeline and next steps

In 2023, the Washington state legislature directed Ecology to conduct an analysis of water use for irrigation, municipal and industrial purposes under the potential scenario of lower Snake River dam removal.

Later in 2023, the federal government made a commitment to complete a similar, but more in-depth study and dedicated over $4 million to the effort. The U.S. Bureau of Reclamation was identified as the lead federal agency for the completion of the analysis and Ecology and the U.S. Bureau of Reclamation agreed to partner on a joint study to conserve resources and align this work.

On December 30, 2024, the U.S. Bureau of Reclamation, in cooperation with Ecology, released the draft Lower Snake River Water Supply Replacement Study. The report received over 1,700 public and peer review comments during the 60-day public review and comment period.

In February 2025, following the close of the comment period, the federal administration terminated the contract that funded the study. Ecology remains committed to completing this important work.

In August 2025, Ecology was able to contract with a consultant to work on finalizing the study. Key tasks remaining include comment review and disposition, possible additional analysis, and completion of a final report. We anticipate finalizing the report by Spring 2026. Other next steps include:

  • Review and categorize comments received on the draft study
  • Conduct additional analysis if needed and within limited state budget
  • Complete and issue final study report

Public Input

The study team’s outreach to water users was an important part of data collection focusing on these areas:

  • Understanding the current water supply situation for irrigation, municipal, and industrial uses, as well as for Tribal users
  • Determining how the current water supply situation might change in a dam breach scenario

This involved individual or small group interviews with water users and representative organizations, initiated after public information sessions in June 2024, and continued through the study’s development. Findings highlight the technical, operational, and economic aspects of water use in the study area.

The U.S. Bureau of Reclamation and Ecology also conducted outreach and engaged with Columbia River Basin Tribes. Tribal leaders and staff were invited to public and Tribal-specific information and project update sessions throughout the various phases of the study. An open invitation was extended for government-to-government consultation and technical staff-to-staff meetings. Consultations were held with Tribes that requested them. The overall goals of the engagement opportunities were to build understanding and incorporate Tribal interests and concerns into the study.

Formal outreach events and open houses to update the public on the study and provide an opportunity to engage with key project team members were provided before and following release of the draft study.