Lefferts Grist Mill Dam Reservoir Report
Nearby: Mill Pond Dam Fresh Pond Dam
Last Updated: January 1, 2026
The Lefferts Grist Mill Dam, located in Suffolk County, New York, is a historic structure with a rich heritage dating back to the year 1800.
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Summary
This privately-owned dam, also known as Lefferts Grist Mill Pond, serves primarily for recreational purposes, offering a serene setting for visitors to enjoy. Standing at a height of 8 feet and stretching over a length of 730 feet, the dam has a storage capacity of 54 acre-feet, providing a surface area of 15 acres for recreational activities.
Managed by the New York State Department of Environmental Conservation (NYS DEC), the Lefferts Grist Mill Dam is regulated, inspected, and enforced to ensure its safety and compliance with state regulations. The dam features an uncontrolled spillway with a width of 15 feet, designed to handle a maximum discharge of 360 cubic feet per second. Despite being classified as having a low hazard potential, the dam's risk assessment is moderate (3), emphasizing the importance of ongoing risk management measures to safeguard the surrounding area and the dam itself.
For water resource and climate enthusiasts, the Lefferts Grist Mill Dam presents an intriguing blend of history, engineering, and environmental stewardship. As a focal point for recreation and a vital piece of local infrastructure, this earth dam serves as a reminder of the importance of balancing human needs with the preservation of natural resources. With its picturesque setting and significant storage capacity, the dam continues to be a valuable asset for the community while requiring careful monitoring and maintenance to ensure its long-term viability in the face of changing environmental conditions.
Year Completed |
1800 |
Dam Length |
730 |
Dam Height |
8 |
River Or Stream |
TR-HUNTINGTON HARBOR |
Primary Dam Type |
Earth |
Surface Area |
15 |
Nid Storage |
54 |
Hazard Potential |
Low |
Nid Height |
8 |
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.
Lefferts Grist Mill Dam
Lloyd Harbor Road 72, Lloyd Harbor