Stone Dam - Dike 4 Reservoir Report

Last Updated: December 21, 2025

Stone Dam - Dike 4, located in Millinocket, Maine, on the West Branch Penobscot River, is a historic structure with a primary purpose of hydroelectric power generation.


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Summary

Built in 1900, this earth dam stands at a height of 9 feet and spans a length of 1240 feet, providing storage of up to 8100 acre-feet of water. With a surface area of 1344 acres and a drainage area of 1890 acres, Stone Dam - Dike 4 plays a crucial role in flood risk reduction, water supply, recreation, and fish and wildlife habitat maintenance.

Despite its age, Stone Dam - Dike 4 has a low hazard potential, according to the Federal Energy Regulatory Commission. While the condition assessment is not currently available, the dam undergoes inspections every three years, with the last one conducted in August 2019. Although there are no outlet gates or spillway, the structure has a spillway width of 0 and a maximum discharge of 0. With its risk assessment rated as high (2), Stone Dam - Dike 4 is closely monitored and managed to ensure its safety and functionality for the surrounding community and environment.

In conclusion, Stone Dam - Dike 4 stands as a testament to early engineering ingenuity, serving as a vital component in water resource management and climate resilience efforts in the Penobscot County area. As a key player in the region's hydroelectric infrastructure, this historic dam continues to play a significant role in balancing multiple purposes, from flood control to recreation, highlighting the importance of sustainable water resource development in the face of changing climate conditions.

Year Completed

1900

Dam Length

1240

Dam Height

9

River Or Stream

West Branch Penobscot River

Surface Area

1344

Drainage Area

1890

Nid Storage

8100

Hazard Potential

Low

Nid Height

9
       
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.