Green Swamp #4 Dam Reservoir Report

Last Updated: December 6, 2025

Green Swamp #4 Dam, located in Passaic, New Jersey, is a concrete structure completed in 1925 primarily used for water supply purposes.


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Summary

Standing at a height of 65 feet and spanning 300 feet in length, this dam plays a crucial role in storing and regulating water from the Wanaque River. With a normal storage capacity of 81,730 acre-feet and covering a surface area of 2,310 acres, it serves as a vital resource for the region, ensuring a reliable water supply for various uses.

Managed by the New Jersey Department of Environmental Protection (NJDEP), Green Swamp #4 Dam is subject to state regulations, inspections, and enforcement to maintain its structural integrity and safety standards. Despite its high hazard potential, the dam's condition assessment in October 2021 reported it to be satisfactory. Regular inspections are conducted every two years to monitor its performance and address any potential risks or issues promptly. Additionally, emergency action plans are in place to ensure preparedness in case of any unforeseen events or emergencies.

With its strategic location in Wanaque Borough and its critical role in water management, Green Swamp #4 Dam stands as a testament to the importance of sustainable water resource management and climate resilience. As climate change continues to impact water systems and availability, structures like this dam play a vital role in ensuring a stable and secure water supply for the community while mitigating potential risks and hazards associated with extreme weather events.

Year Completed

1925

Dam Length

300

Dam Height

65

River Or Stream

Wanaque River

Primary Dam Type

Concrete

Surface Area

2310

Drainage Area

90.4

Nid Storage

81730

Hazard Potential

High

Nid Height

65
       
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.