West Fork Bitterroot (painted Rocks)

About West Fork Bitterroot (painted Rocks)

The primary purpose of West Fork Bitterroot (painted Rocks) is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by State Water Projects (state). It impounds the West Fork Of Bitterroot near Darby.

The dam stands 143 feet tall and stretches 800 feet across, creates a reservoir covering 655 acres, has a maximum storage capacity of 45,100 acre-feet, and collects water from a drainage area of 316 square miles. Completed in 1940, the structure is well-established, with more than 75 years of service.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. An emergency action plan is in place for this dam. The most recent inspection on record was 06/18/2024.

At 143 feet, this dam is taller than 99% of all dams in the United States.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Montana dam safety program can provide more specific information about emergency planning for this structure.

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