Errol Reservoir Report

Last Updated: December 20, 2025

Errol is a hydroelectric dam located in the picturesque town of Errol, New Hampshire, along the Androscoggin River.


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Summary

Built in 1887, this historic structure stands at 25 feet tall and spans 205 feet in length. With a storage capacity of 80,000 acre-feet and a maximum discharge of 19,700 cubic feet per second, Errol plays a crucial role in providing renewable energy to the region.

Managed by the NHDES Dam Bureau and regulated by the Federal Energy Regulatory Commission, Errol is subject to regular inspections and enforcement measures to ensure its safety and efficiency. Despite its low hazard potential, the dam is classified as having a very high risk due to its age and the potential consequences of failure. Emergency action plans are in place to address any unforeseen events, with 11 slide gates controlling water flow through the spillway.

For water resource and climate enthusiasts, Errol serves as a fascinating example of the intersection between history, infrastructure, and environmental stewardship. Its role in generating clean energy and managing water resources highlights the importance of sustainable practices in our ever-changing climate. As we look towards the future, understanding and safeguarding structures like Errol will be essential in ensuring a resilient and secure water supply for generations to come.

Year Completed

1887

Dam Length

205

Dam Height

25

River Or Stream

Androscoggin River

Surface Area

7850

Drainage Area

1045

Nid Storage

80000

Outlet Gates

Slide (sluice gate) - 11

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

25
       
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.
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