Mystic Dike

About Mystic Dike

The primary purpose of Mystic Dike is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Northwestern Energy (private). It impounds the West Rosebud Creek near Fishtail, Mt.

The dam stands 21 feet tall and stretches 145 feet across, creates a reservoir covering 446 acres, has a maximum storage capacity of 21,000 acre-feet, and collects water from a drainage area of 52 square miles. Completed in 1927, 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 satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 09/30/2020.

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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