Greenwood Lake Dam Reservoir Report

Last Updated: December 6, 2025

Greenwood Lake Dam, located in West Milford Township, New Jersey, is a concrete gravity dam on the Wanaque River with a primary purpose of recreation.


°F

°F

mph

Wind

%

Humidity

Summary

Completed in 1928, the dam stands at a height of 17 feet and stretches 270 feet in length, providing a storage capacity of 13,269 acre-feet and covering a surface area of 1,733 acres. The dam is owned and regulated by the state of New Jersey, specifically by the New Jersey Department of Environmental Protection (NJDEP), ensuring that it undergoes regular inspections and enforcement measures to maintain its fair condition.

Despite its fair condition, Greenwood Lake Dam has a high hazard potential, prompting a biennial inspection frequency to assess its safety and functionality. The dam's emergency action plan (EAP) was last revised in July 2018, with no recent updates on its compliance with guidelines or the preparation of inundation maps. While there are no outlet gates or associated structures linked to the dam, its proximity to residential areas and the risk of inundation highlights the importance of ongoing risk management measures and a thorough assessment of potential hazards to ensure the safety of the surrounding communities and water resources.

Year Completed

1928

Dam Length

270

Dam Height

17

River Or Stream

Wanaque River

Primary Dam Type

Concrete

Surface Area

1733

Drainage Area

27.1

Nid Storage

13269

Hazard Potential

High

Nid Height

17
       
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.