Lake Tappan Dike Reservoir Report

Last Updated: December 11, 2025

Lake Tappan Dike, located in Old Tappan, New Jersey, is a privately owned earth dam that serves as a crucial water supply structure along the Hackensack River.


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Summary

With a dam height of 20 feet and a length of 2500 feet, the dike has a storage capacity of 8000 acre-feet, providing essential water resources for the region. The dam has a low hazard potential and is not currently rated for condition assessment.

Managed by the New Jersey Department of Environmental Protection, Lake Tappan Dike is subject to state regulation, permitting, inspection, and enforcement to ensure its safety and functionality. The dam, completed in an unspecified year, covers a surface area of 560 acres and has a drainage area of 49.4 square miles. Despite its critical role in water supply, the dam has not been modified in recent years and lacks detailed risk assessment measures or emergency action plans.

Congressional District 05, represented by Josh S. Gottheimer, oversees the area where Lake Tappan Dike is situated, underscoring the importance of maintaining the dam's integrity for water resource sustainability and climate resilience. As a significant infrastructure for water management in Bergen County, this dike stands as a testament to the intricate balance between human development and environmental conservation in the face of changing climate patterns and water resource demands.

Dam Length

2500

Dam Height

20

River Or Stream

Hackensack River

Primary Dam Type

Earth

Surface Area

560

Drainage Area

49.4

Nid Storage

8000

Hazard Potential

Low

Nid Height

20
       
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.