Supplemental Environmental Impact Statement for Near-term Colorado River Operations

The Bureau of Reclamation has released the final Supplemental Environmental Impact Statement for Near-term Colorado River Operations. The supplement is to the December 2007 Record of Decision associated with the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead, referred to as the 2007 Interim Guidelines.

For more information on the public involvement process and to view submitted comments on the Revised Draft SEIS, visit our Public Involvement page or click the link in the left menu.

Key Updates to the Revised Draft SEIS

In March 2024, Reclamation released the final SEIS for the near-term operation of Glen Canyon and Hoover dams. These new interim operating guidelines are specifically designed to manage the dams at lower elevations and prevent water levels at Lake Powell and Lake Mead from further declining in order to maintain congressionally authorized infrastructure, operations, water deliveries and power generation.

On April 14, 2023, the original draft SEIS was issued, and two key developments occurred that require reassessment of the range of alternatives: improved hydrology and a proposal for a new alternative.

  1. Hydrology in the Colorado River Basin has improved compared with the hydrology at the time the SEIS analysis began in December 2022. Analysis in the original draft SEIS was based on hydrology from September 2022. Using improved hydrology from June 2023, the percent of traces declined below critical elevations at Lake Powell (i.e., below 3,490 feet) and Lake Mead through 2026.
  2. In May 2023, the Lower Division States proposed an alternative for approximately 3 million acre-feet of water to be conserved to protect critical levels at Lake Mead ("Lower Division Proposal") (Lower Basin Plan Letter - May 22, 2023). The Upper Division States recommended that this proposed alternative be analyzed in the NEPA process (Seven States Letter - May 22, 2023). After the Lower Division Proposal was submitted, Reclamation temporarily withdrew the original draft SEIS so that it could fully analyze the effects of the proposal under the NEPA.

On October 2023, Reclamation issued a revised draft SEIS after assessing the effects of those developments and conducting modeling analysis of the No Action Alternative, Action Alternative 1, Action Alternative 2, and the Lower Division Proposal with updated hydrology. This was described in Attachment B-1 to Appendix B. The results of that modeling analysis indicate that the risk of reaching critical elevations at Lake Powell and Lake Mead has been reduced substantially by hydrology.

Based on these modeling results, Reclamation continued the SEIS process with detailed consideration of the No Action Alternative and the Lower Division Proposal. The Lower Division Proposal was designated as the Proposed Action. Action Alternatives 1 and 2 were addressed as alternatives considered but eliminated from detailed analysis.

Purpose and Need

The purpose of the SEIS is to supplement the 2007 Interim Guidelines to modify guidelines for operation of Glen Canyon Dam and Hoover Dam to address historic drought, historically low reservoirs, and low runoff conditions in the Colorado River Basin. The need for the modified operating guidelines is based on the potential that continued low runoff conditions in the Colorado River Basin could lead Lake Powell and Lake Mead to decline to critically low elevations, impacting operations through the remainder of the interim period (prior to January 1, 2027).


The final SEIS analyzes two alternatives in detail:

  • The No Action Alternative, required by the National Environmental Policy Act, describes the continued implementation of existing agreements that control operations of Glen Canyon and Hoover Dams.
  • The Proposed Action ("Lower Division Proposal"), which is the Preferred Alternative, models changes to operations for both Glen Canyon Dam and Hoover Dam. The Proposed Action includes assumptions for reducing releases, if needed, down to 6.0 million acre-feet from Lake Powell with the goal of keeping Lake Powell elevation above 3,500 feet and assumptions for a total of 3 maf of SEIS conservation through 2026 with a minimum of 1.5 million acre-feet physically conserved by the end of calendar year 2024. Under the Proposed Action, tier-based reductions and contributions shall be limited to the existing 2007 Interim Guidelines, Lower Basin DCP, and Minute 323.


For further information, contact the project team by email at

Last Updated: 3/5/24