Mill Dam Reservoir Report

Last Updated: December 6, 2025

Mill Dam, located in Mount Holly, New Jersey, is a local government-owned structure on the North Branch Rancocas Creek.


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Summary

Built in 1908, this earth-type dam stands at a height of 14.6 feet and spans 240 feet in length, with a storage capacity of 102 acre-feet. Its primary purpose is for recreation, offering a surface area of 37 acres for outdoor activities.

The dam is state-regulated by the New Jersey Department of Environmental Protection, with inspection and enforcement protocols in place to ensure its safety and functionality. Despite being classified as having low hazard potential, the dam's condition assessment in 2007 indicated it was in fair condition. With a drainage area of 144 square miles and a maximum discharge of 78 cubic feet per second, Mill Dam plays a crucial role in managing water resources in the region.

For water resource and climate enthusiasts, Mill Dam serves as a significant structure within the local ecosystem, providing recreational opportunities while also contributing to the management of water flow and storage. Its historical significance, combined with its ongoing regulatory oversight and maintenance, highlights the intersection of human intervention and natural resources in the face of changing environmental conditions.

Year Completed

1908

Dam Length

240

Dam Height

14.6

River Or Stream

North Branch Rancocas Creek

Primary Dam Type

Earth

Surface Area

37

Drainage Area

144

Nid Storage

102

Hazard Potential

Low

Nid Height

15
       
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.