Upper Lake Dam Reservoir Report

Last Updated: January 2, 2026

Upper Lake Dam, located in Yaphank, Suffolk County, New York, stands as a vital structure on the Carman River, serving primarily for recreational purposes since its completion in 1932.


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Summary

Managed by the local government, the dam boasts an earth design with a height of 8 feet and a length of 250 feet, offering a maximum storage capacity of 68 acre-feet. Despite its low hazard potential, the dam's spillway width of 8 feet allows for a maximum discharge of 35 cubic feet per second, ensuring effective water management during peak flow events.

State-regulated by the NYS DEC, Upper Lake Dam undergoes regular inspections, with the last recorded assessment in May 2009. While its condition remains unrated, the risk assessment categorizes the dam as moderate, emphasizing the need for proactive risk management measures. With its scenic location and modest surface area of 19 acres, the dam plays a crucial role in enhancing the local ecosystem and providing a recreational haven for residents and visitors alike. As climate change impacts water resources, the sustainable management of Upper Lake Dam will be pivotal in adapting to evolving hydrological patterns and safeguarding the surrounding environment for future generations.

Year Completed

1932

Dam Length

250

Dam Height

8

River Or Stream

CARMANS RIVER

Primary Dam Type

Earth

Surface Area

19

Nid Storage

68

Hazard Potential

Low

Nid Height

8
       
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.