Loon Lake Dam Reservoir Report

Last Updated: December 14, 2025

Loon Lake Dam, also known as The Overflow, is a privately owned structure located in Croydon, Sullivan County, New Hampshire.


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Summary

Built in 1961, this earth dam stands at a height of 15 feet and has a length of 100 feet, serving primarily for recreational purposes. Situated on Long Pond Brook, the dam has a storage capacity of 328 acre-feet and a surface area of 57 acres, making it an important resource for water enthusiasts in the region.

Managed by the NHDES Dam Bureau, Loon Lake Dam is subject to state regulation, inspection, and enforcement to ensure its safety and functionality. The dam's hazard potential is considered significant, with a fair condition assessment as of August 2017. Despite moderate risk and a spillway type of "uncontrolled," the dam continues to provide recreational opportunities for visitors. With a risk management plan in place and regular inspections, the dam is maintained to meet safety guidelines and protect the surrounding area from potential inundation.

For water resource and climate enthusiasts, Loon Lake Dam offers a fascinating case study of a privately owned earth dam that not only serves recreational purposes but also plays a crucial role in managing water resources in Sullivan County, New Hampshire. With its unique design and significant hazard potential, the dam highlights the importance of proper regulation, inspection, and risk management measures to ensure the safety and sustainability of such structures in the face of changing climate conditions.

Year Completed

1961

Dam Length

100

Dam Height

15

River Or Stream

LONG POND BROOK

Primary Dam Type

Earth

Surface Area

57

Drainage Area

8

Nid Storage

328

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

15
       
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.