Main Mill Dam Reservoir Report

Last Updated: December 19, 2025

Main Mill Dam, also known as Imperial Dam, is a historic structure located in Plattsburgh, New York, along the Saranac River.


°F

°F

mph

Wind

%

Humidity

Summary

Built in 1881, this concrete dam stands at a height of 25 feet and spans 715 feet, with a storage capacity of 920 acre-feet. Primarily used for hydroelectric purposes, the dam is owned by a private entity and is regulated by the New York State Department of Environmental Conservation.

Despite its age and significant storage capacity, Main Mill Dam has been assessed with a poor condition and a high hazard potential. The last inspection in September 2020 revealed the dam's structural deficiencies, prompting concerns about its safety and the potential risks it poses to downstream areas. With a very high risk rating of 1, it is crucial for ongoing risk management measures to be implemented to ensure the dam's integrity and the safety of surrounding communities.

As water resource and climate enthusiasts, the data on Main Mill Dam serves as a reminder of the importance of maintaining and monitoring aging infrastructure to prevent potential disasters. With its rich history and critical role in providing hydroelectric power, Main Mill Dam stands as a testament to the intersection of human ingenuity and environmental stewardship. Efforts to address its poor condition and high hazard potential will be essential in safeguarding both the dam's structural integrity and the surrounding ecosystem.

Year Completed

1881

Dam Length

715

Dam Height

25

River Or Stream

SARANAC RIVER

Primary Dam Type

Concrete

Surface Area

84

Drainage Area

608

Nid Storage

920

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.