Lake Garrison Dam Reservoir Report

Last Updated: December 5, 2025

Lake Garrison Dam, located in Porchtown, New Jersey, was completed in 1924 for the primary purpose of recreation.


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Summary

This private-owned dam stands at a height of 6.8 feet and has a length of 500 feet, impounding the Reed Branch of Still Run to create a surface area of 33 acres. The dam has a normal storage capacity of 89 acre-feet and a maximum storage of 152 acre-feet, serving as a crucial water resource for the surrounding area.

Despite its historical significance and recreational value, Lake Garrison Dam is currently rated as having a poor condition assessment with a significant hazard potential. The dam is regulated by the New Jersey Department of Environmental Protection (NJDEP) and undergoes regular inspections, with the last one conducted in December 2020. With its location in Elk Township and close proximity to Congressional District 02, the dam plays a crucial role in water management and flood control for the region, highlighting the importance of ongoing maintenance and safety measures to ensure its long-term sustainability and resilience in the face of changing climate conditions.

Year Completed

1924

Dam Length

500

Dam Height

6.8

River Or Stream

Reed Branch of Still Run

Primary Dam Type

Earth

Surface Area

33

Drainage Area

7

Nid Storage

152

Hazard Potential

Significant

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.