Mirror Lake Dam Reservoir Report

Last Updated: December 16, 2025

Mirror Lake Dam, located in Woodstock, New Hampshire, was completed in 1836 and serves as a vital recreational resource for the area.


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Summary

With a height of 11.5 feet and a length of 290 feet, the dam holds a maximum storage capacity of 187 acre-feet, making it a significant feature along TR Hubbard Brook. Despite its historical significance, the dam has been assessed as being in poor condition with a high hazard potential, prompting concerns for its long-term safety and maintenance.

Managed by the NHDES Dam Bureau, Mirror Lake Dam is subject to state regulation, inspection, and enforcement to ensure its continued operation and safety. The dam's primary purpose is recreation, offering a serene surface area of 38 acres for visitors to enjoy. However, with a moderate risk assessment rating of 3, there is a need for ongoing risk management measures to address potential hazards and safeguard the surrounding community and environment. As climate change continues to impact water resources, the resilience and sustainability of Mirror Lake Dam will be crucial for preserving this important waterway for future generations.

Year Completed

1836

Dam Length

290

Dam Height

11.5

River Or Stream

TR HUBBARD BROOK

Primary Dam Type

Earth

Surface Area

38

Drainage Area

0.34

Nid Storage

187

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

12
       
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.