Purity Lake Dam Reservoir Report

Last Updated: December 14, 2025

Purity Lake Dam, located in Madison, New Hampshire, serves as a recreational resource for visitors to the area.


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Summary

Built in 1750, this earth dam stands at a height of 13.2 feet and has a storage capacity of 182 acre-feet, making it an essential feature of the surrounding landscape. The dam regulates the flow of water from the Danforth Ponds, providing opportunities for boating, fishing, and other water-based activities.

Despite its historical significance and recreational value, Purity Lake Dam is classified as having a high hazard potential and poor condition assessment. The last inspection in June 2020 revealed the need for improvement in maintenance and safety measures. With a moderate risk assessment rating, it is crucial for the dam's owners to prioritize risk management measures to ensure the safety of the surrounding community and maintain the dam's functionality for future generations. Additionally, the dam is regulated by the New Hampshire Department of Environmental Services Dam Bureau, indicating a commitment to monitoring and oversight to address potential issues proactively.

For water resource and climate enthusiasts, Purity Lake Dam represents both a historical landmark and a critical piece of infrastructure for recreational purposes. Its location in a picturesque setting in Carroll County, New Hampshire, offers a unique opportunity to appreciate the intersection of human engineering with natural beauty. As efforts continue to address the dam's maintenance needs and ensure its long-term viability, stakeholders can work together to preserve this valuable resource for the enjoyment of all who visit the area.

Year Completed

1750

Dam Length

96

Dam Height

13.2

River Or Stream

DANFORTH PONDS

Primary Dam Type

Earth

Surface Area

27

Drainage Area

6.76

Nid Storage

182

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

13
       
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.