Deferiet Reservoir Report
Nearby: Herrings West End Dam
Last Updated: December 18, 2025
Deferiet, located in Jefferson County, New York, is home to a historic hydroelectric dam on the Black River.
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Summary
Built in 1899, this buttress dam stands at a height of 18 feet and spans 695 feet in length, with a storage capacity of 405 acre-feet. The dam serves the primary purpose of hydroelectric power generation and is regulated by the Federal Energy Regulatory Commission.
The dam's spillway, with a width of 522 feet, is uncontrolled, and the hazard potential is classified as low. Although the condition assessment is not available, the risk assessment is moderate. The last inspection was conducted in August 2019, with an inspection frequency of 3 years. The emergency action plan was last revised in December 2013, and there are no associated structures or locks with the dam.
Despite its age, the Deferiet dam continues to play a crucial role in providing renewable energy and water resource management in the area. With its rich history and ongoing operation, the dam serves as a testament to the enduring impact of hydroelectric infrastructure on local communities and the environment.
Year Completed |
1899 |
Dam Length |
695 |
Dam Height |
18 |
River Or Stream |
Black River |
Primary Dam Type |
Buttress |
Surface Area |
70 |
Drainage Area |
1817 |
Nid Storage |
405 |
Hazard Potential |
Low |
Foundations |
Rock |
Nid Height |
18 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Deferiet