Swannanoa Lake #1 (South) Dam Reservoir Report

Last Updated: December 9, 2025

Swannanoa Lake #1 (South) Dam, located in Jefferson Township, Morris County, New Jersey, was completed in 1914 with a primary purpose of recreation.


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Summary

This masonry dam stands at a height of 15 feet and spans 228 feet in length, creating a reservoir with a storage capacity of 400 acre-feet. The dam is situated on the West Branch Rockaway River and is regulated by the New Jersey Department of Environmental Protection.

Despite its age, the dam is in satisfactory condition, with a high hazard potential due to its location and storage capacity. Regular inspections are conducted, with the last assessment completed in July 2021. The dam has a designated emergency action plan (EAP) with a recent revision in December 2021 to ensure readiness in case of a potential hazard or failure. The surrounding area has a drainage area of 13.9 square miles, and the reservoir covers 51 acres, providing a recreational space for the community while also serving important water resource management functions.

Year Completed

1914

Dam Length

228

Dam Height

15

River Or Stream

West Branch Rockaway River

Primary Dam Type

Masonry

Surface Area

51

Drainage Area

13.9

Nid Storage

400

Hazard Potential

High

Nid Height

15
       
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.