Macopin Reservoir Dam Reservoir Report

Last Updated: December 9, 2025

The Macopin Reservoir Dam, located in West Milford Township, New Jersey, is a stone dam completed in 1892 for the primary purpose of water supply.


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Summary

It stands at a height of 34 feet and has a length of 434 feet, with a storage capacity of 206 acre-feet and a drainage area of 63.7 square miles. The dam, built on the Pequannock River, is owned by the local government and regulated by the New Jersey Department of Environmental Protection, with state permitting and inspection in place.

Despite being designated as having a high hazard potential, the Macopin Reservoir Dam is currently assessed as satisfactory in condition, with the last inspection conducted in April 2021. The dam has a regular inspection frequency of every 2 years, and emergency action plans are in place, although their last revision was in December 2020. With a maximum discharge capacity of 17,600 cubic feet per second, the dam plays a crucial role in managing water resources in the region and ensuring the safety of surrounding communities in the event of emergencies.

Overall, the Macopin Reservoir Dam serves as a vital infrastructure for water supply in Morris County, New Jersey, with its historical significance dating back to the late 19th century. As a stone dam with a high hazard potential, it is subject to rigorous regulatory oversight and maintenance to ensure its continued functionality and safety. Climate enthusiasts and water resource experts can appreciate the dam's role in managing water resources and its importance in safeguarding the local environment and population from potential risks associated with its operation.

Year Completed

1892

Dam Length

434

Dam Height

34

River Or Stream

Pequannock River

Primary Dam Type

Stone

Surface Area

12

Drainage Area

63.7

Nid Storage

206

Hazard Potential

High

Nid Height

34
       
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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.