Stillwater Reservoir Report

Last Updated: December 20, 2025

Stillwater, located in Orono, Maine, is a privately owned concrete gravity dam on the Stillwater River that was completed in 1902 for hydroelectric power generation and recreation purposes.


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Summary

With a height of 25 feet and a length of 1720 feet, Stillwater has a storage capacity of 1910 acre-feet and serves a drainage area of 7602 square miles. The dam's spillway, which is uncontrolled, has a width of 908 feet and a maximum discharge of 25000 cubic feet per second.

Despite its age, Stillwater has a low hazard potential and a moderate risk assessment rating of 3. It is regulated by the Federal Energy Regulatory Commission, which also oversees its inspections. The dam's emergency action plan was last revised in December 2018, ensuring that necessary measures are in place in case of emergencies. While the condition assessment of Stillwater is not available, its overall risk management measures are deemed sufficient for its continued operation. For water resource and climate enthusiasts, Stillwater serves as a historical and functional example of sustainable hydroelectric infrastructure in the New England District.

Year Completed

1902

Dam Length

1720

Dam Height

25

River Or Stream

Stillwater River

Primary Dam Type

Concrete

Surface Area

191

Drainage Area

7602

Nid Storage

1910

Hazard Potential

Low

Nid Height

25
       
Seasonal Comparison

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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.