Lake Deforest Dam Reservoir Report

Last Updated: January 1, 2026

Lake Deforest Dam, located in West Nyack, New York, is a vital water resource infrastructure managed by a public utility.


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Summary

Completed in 1956, this earth dam stands at a height of 40 feet and spans 1330 feet across the Hackensack River. With a storage capacity of 36,362 acre-feet and a surface area of 900 acres, Lake Deforest Dam plays a crucial role in water supply for the region, storing up to 17,250 acre-feet of water for domestic and agricultural use.

Despite its importance, Lake Deforest Dam poses a high hazard potential due to its location and the volume of water it holds. While its condition remains unrated, regular inspections are conducted to ensure its structural integrity and safety. The dam is equipped with a controlled spillway, 109 feet wide, to manage excess water flow and prevent flooding downstream. In case of emergencies, an Emergency Action Plan (EAP) is in place, with the last revision completed in July 2020.

For water resource and climate enthusiasts, Lake Deforest Dam serves as a prime example of essential infrastructure for water supply and flood control. With its high hazard potential and very high risk assessment, continued monitoring and maintenance are crucial to safeguard the surrounding communities and ensure the dam's functionality. As a key component of the regional water management system, Lake Deforest Dam highlights the intersection of infrastructure, environmental conservation, and public safety in the face of changing climate conditions.

Year Completed

1956

Dam Length

1330

Dam Height

40

River Or Stream

HACKENSACK RIVER

Primary Dam Type

Earth

Surface Area

900

Drainage Area

26.6

Nid Storage

36362

Hazard Potential

High

Nid Height

40
       
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.