Grandmother

About Grandmother

The primary purpose of Grandmother 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 Pca Hydro Inc. (private). It impounds the Wisconsin River near Merrill.

The dam stands 39 feet tall and stretches 724 feet across, creates a reservoir covering 758 acres, has a maximum storage capacity of 1,940 acre-feet, and collects water from a drainage area of 2,269 square miles. Completed in 1923, the structure is over a century old.

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 fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 09/13/2022.

At 39 feet, this dam is taller than 86% of dams nationwide.

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 Wisconsin dam safety program can provide more specific information about emergency planning for this structure.

Search for dams near your address to see all dams in your area with hazard classifications and safety data.