Grand Lake (Matagamon) Reservoir Report

Last Updated: January 12, 2026

Grand Lake (Matagamon) in Maine is a private hydroelectric reservoir situated on the Penobscot River.


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Summary

With a concrete dam standing at a height of 25 feet and a length of 218 feet, the reservoir boasts a storage capacity of 45,800 acre-feet and a surface area of 4,200 acres. Completed in 1941, this dam serves multiple purposes, including hydroelectric power generation.

Despite its historical significance and functional importance, Grand Lake is in a state of disrepair, with a poor condition assessment and a high hazard potential. The last inspection conducted in July 2020 revealed its deteriorating state, prompting concerns about its safety and structural integrity. With the dam being under state regulation and subject to regular inspection, there are ongoing efforts to address its maintenance and safety issues to ensure the protection of the surrounding community and water resources.

As climate change continues to impact water resources and infrastructure, the management and maintenance of dams like Grand Lake are crucial for safeguarding against potential risks and ensuring the sustainable use of water for future generations. With a focus on improving its condition and addressing safety concerns, Grand Lake represents a significant case study in the intersection of water resource management and climate adaptation efforts.

Year Completed

1941

Dam Length

218

Dam Height

25

River Or Stream

Penobscot River

Primary Dam Type

Concrete

Surface Area

4200

Hydraulic Height

15

Drainage Area

485

Nid Storage

45800

Structural Height

25

Hazard Potential

High

Nid Height

25
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.