Diamond Island Diversion Dam Reservoir Report

Last Updated: December 5, 2025

Diamond Island Diversion Dam, located in Watertown, New York, is a concrete structure built in 1914 for hydroelectric purposes on the Black River.


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Summary

Standing at a height of 13 feet and stretching 710 feet in length, this dam has a normal storage capacity of 134 acre-feet and a maximum discharge of 52,000 cubic feet per second. With a spillway width of 775 feet, the dam is equipped with uncontrolled spillways to manage excess water flow.

Managed by a Public Utility entity and regulated by the New York State Department of Environmental Conservation, Diamond Island Diversion Dam poses a low hazard potential and has not been rated for its current condition. Despite being last inspected in 1998, the dam is considered to have a moderate risk level (3) based on its location and structural specifications. While emergency preparedness measures such as an Emergency Action Plan and risk management strategies are not explicitly mentioned in the available data, the dam continues to serve its purpose efficiently within the region.

For water resource and climate enthusiasts, Diamond Island Diversion Dam serves as a vital infrastructure for hydroelectric power generation in Jefferson County, New York. Its historical significance, combined with its role in water management on the Black River, highlights the importance of maintaining and monitoring such structures to ensure the safety of surrounding communities and the sustainability of the region's water resources.

Year Completed

1914

Dam Length

710

Dam Height

13

River Or Stream

BLACK RIVER

Primary Dam Type

Concrete

Surface Area

31

Drainage Area

1888.5

Nid Storage

134

Hazard Potential

Low

Nid Height

13
       
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.