Lake Cohasset Upper Dam Reservoir Report

Last Updated: December 6, 2025

Lake Cohasset Upper Dam, located in Arden, New York, is a concrete structure completed in 1924 primarily for recreation purposes.


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Summary

The dam stands at a height of 25 feet and spans 150 feet, providing a storage capacity of 373 acre-feet. With a surface area of 37 acres and drainage area of 1.55 square miles, the dam regulates the flow of Arden Brook.

Despite its recreational significance, Lake Cohasset Upper Dam poses a high hazard potential with a poor condition assessment. The dam lacks a spillway, increasing the risk of flooding in the event of overflow. The last inspection in October 2019 revealed the need for urgent maintenance and repair. The New York State Department of Environmental Conservation oversees the regulation, inspection, and enforcement of safety measures at the dam.

As water resource and climate enthusiasts monitor the state of Lake Cohasset Upper Dam, concerns about its structural integrity and emergency preparedness persist. With a high-risk classification and outdated emergency action plan, stakeholders must prioritize the implementation of risk management measures to ensure the safety of downstream communities and the preservation of the surrounding ecosystem.

Year Completed

1924

Dam Length

150

Dam Height

25

River Or Stream

ARDEN BROOK

Primary Dam Type

Concrete

Surface Area

37

Drainage Area

1.55

Nid Storage

373

Hazard Potential

High

Nid Height

25
       
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.