May Pond Dam Reservoir Report

Last Updated: December 14, 2025

May Pond Dam, also known as Butterfields Pond Dam, is a state-owned structure located in Washington, New Hampshire.


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Summary

Built in 1830, this earth dam stands at a height of 14 feet and stretches 215 feet in length, impounding the waters of the Ashuelot River for recreational purposes. The dam has a storage capacity of 950 acre-feet, with a normal storage level of 465 acre-feet across a surface area of 158 acres.

Managed by the NHDES Dam Bureau, May Pond Dam has a state-regulated status with inspection, permitting, and enforcement protocols in place. Despite being classified as having a significant hazard potential, the dam's condition has been assessed as fair as of October 2016. With a moderate risk assessment rating, the dam is equipped with a 63-foot uncontrolled spillway and has a maximum discharge capacity of 1071 cubic feet per second. This historical structure continues to play a vital role in water resource management and recreation within the region.

Year Completed

1830

Dam Length

215

Dam Height

14

River Or Stream

ASHUELOT RIVER

Primary Dam Type

Earth

Surface Area

158

Drainage Area

6.84

Nid Storage

950

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

14
       
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.