Hempstead Lake Dam Reservoir Report
Last Updated: January 2, 2026
Hempstead Lake Dam, located in Rockville Centre, Nassau County, New York, serves as a crucial structure for recreational purposes, providing a serene environment for visitors to enjoy.
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Summary
Built in 1873, this earth dam stands at a height of 24 feet and stretches over 1200 feet, with a storage capacity of 1220 acre-feet and a surface area of 149 acres. The dam controls the flow of the Mill River and has a spillway width of 24 feet, ensuring the proper management of water levels and preventing potential flooding in the area.
Despite its historical significance, the dam's condition assessment in 2006 deemed it to be in poor condition, with a high hazard potential. Regular inspections are conducted, with the last one taking place in November 2020, to monitor its structural integrity and safety. Although the risk assessment categorizes the dam's risk level as moderate, there is a need for continued monitoring and potential risk management measures to ensure the safety of surrounding communities and the preservation of this important water resource. Climate enthusiasts and water resource advocates should stay informed about the ongoing maintenance efforts and potential improvements to safeguard this vital infrastructure.
Year Completed |
1873 |
Dam Length |
1200 |
Dam Height |
24 |
River Or Stream |
MILL RIVER |
Primary Dam Type |
Earth |
Surface Area |
149 |
Drainage Area |
14.9 |
Nid Storage |
1220 |
Hazard Potential |
High |
Nid Height |
24 |
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.
Hempstead Lake Dam
Lakeside Drive Hempstead