Mountain Lake Dam Reservoir Report

Last Updated: December 14, 2025

Mountain Lake Dam, located in Carroll, New Hampshire, is a state-regulated structure managed by the NHDES Dam Bureau.


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Summary

Situated on Hanson Brook, this concrete dam primarily serves recreational purposes, offering a surface area of 12 acres and a maximum storage capacity of 143 acre-feet. With a structural height of 11 feet and a length of 150 feet, the dam has a low hazard potential and is assessed to be in fair condition as of 2013.

Despite its moderate risk assessment, Mountain Lake Dam has a low hazard potential and is inspected every 6 years to ensure its safety and functionality. The dam features an uncontrolled spillway with a width of 18 feet, capable of handling a maximum discharge of 1020 cubic feet per second. Although no outlet gates or associated structures are listed, the dam's emergency action plan status and risk management measures are not specified, indicating room for improvement in emergency preparedness and response protocols.

Overall, Mountain Lake Dam is a vital infrastructure for recreational activities in the area, but stakeholders may benefit from enhancing their emergency preparedness measures and risk management strategies to mitigate potential hazards and ensure the long-term safety and sustainability of the dam for water resource and climate enthusiasts.

Dam Length

150

Dam Height

11

River Or Stream

HANSON BROOK

Primary Dam Type

Concrete

Surface Area

12

Drainage Area

0.93

Nid Storage

143

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

11
       
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.