Cliff Lake Reservoir Report

Last Updated: December 7, 2025

Cliff Lake, located in Sullivan County, New York, is a privately owned hydroelectric facility with a primary purpose of generating power.


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Summary

Constructed in 1930 by Chas. T. Main, Inc., this concrete dam stands at 36 feet high and stretches 610 feet in length, holding a maximum storage capacity of 2,873 acre-feet. The reservoir covers an area of 190 acres and is fed by the Mongaup River, with a drainage area of 30 square miles.

With a high hazard potential due to its size and location, Cliff Lake is under the jurisdiction of the Federal Energy Regulatory Commission for regulation and inspections. While the dam has not been modified in recent years, it is subject to regular inspections to ensure its structural integrity. The facility also serves recreational purposes in addition to hydroelectric power generation, making it a significant contributor to the local water resource management and climate adaptation efforts in the region.

Year Completed

1930

Dam Length

610

Dam Height

36

River Or Stream

Mongaup River

Primary Dam Type

Concrete

Surface Area

190

Drainage Area

30

Nid Storage

2873

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

36
       
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.