Grand Lake (matagamon)

About Grand Lake (matagamon)

The primary purpose of Grand Lake (matagamon) 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 Mattagamon Lake Association (private). It impounds the Penobscot River.

The dam stands 25 feet tall and stretches 218 feet across, creates a reservoir covering 4,200 acres, has a maximum storage capacity of 45,800 acre-feet, and collects water from a drainage area of 485 square miles. Completed in 1941, 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 11/12/2021.

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 Maine 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.