Upper Twin Lakes Dam Reservoir Report

Last Updated: December 6, 2025

The Upper Twin Lakes Dam in Pompton Lakes, New Jersey, is a private dam that serves primarily for recreation purposes.


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Summary

Situated on Irish Brook, this earth and gravity dam stands at a height of 7 feet and stretches 270 feet in length. With a storage capacity of 61 acre-feet and a surface area of 20 acres, it provides a picturesque setting for outdoor activities in the Wanaque Borough.

Despite its low hazard potential, the dam's condition assessment is rated as poor, with the last inspection conducted in August 2018. It is regulated by the New Jersey Department of Environmental Protection and undergoes regular inspections, permitting, and enforcement to ensure public safety. The dam's emergency action plan was last revised in October 2010, and risk management measures are in place to mitigate any potential threats.

Water resource and climate enthusiasts will appreciate the vital role that the Upper Twin Lakes Dam plays in providing recreational opportunities while also highlighting the importance of proper maintenance and monitoring to ensure its structural integrity and safety for the surrounding community. As part of the Philadelphia District, this dam represents a balance between human enjoyment of natural resources and the need for responsible infrastructure management in the face of changing environmental conditions.

Dam Length

270

Dam Height

7

River Or Stream

Irish Brook

Primary Dam Type

Earth

Surface Area

20

Drainage Area

6.8

Nid Storage

61

Hazard Potential

Low

Nid Height

7
       
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.