Lefferts Grist Mill Dam dam
Lefferts Grist Mill Dam
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. 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.
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.
- 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.
- 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.
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, environmental 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.
Plan around the weather
Same NOAA / yr.no feed Snoflo's iOS app uses. Watch the precipitation column on the meteogram -- rain on the basin upstream typically lifts inflow 24-72 hours later.
Next 5 days, hour by hour
Temperature line with weather symbols on top, snow + rain accumulation as columns, humidity as a dotted line.
5-day forecast table
Every 3 hours, broken out across temperature, snow, rain, humidity, and wind. Each cell is colour-coded relative to the column min/max.
| Time | Condition | Temp (°F) | Snow (in) | Rain (in) | Humidity (%) | Wind (mps) | Wind dir |
|---|---|---|---|---|---|---|---|
| Loading detailed forecast… | |||||||
15-day temperature & precipitation
Daily temperatures, snow, and rain projected over the next two weeks.
Nearby streamflow gauges
USGS streamgauges around Lefferts Grist Mill Dam -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Cold Spring Brook At Cold Spring Harbor Ny | 2 cfs | → |
| Nissequogue River Near Smithtown Ny | 31 cfs | → |
| Rippowam River At Stamford | 11 cfs | → |
| Carlls River At Babylon Ny | 15 cfs | → |
| Massapequa Creek At Massapequa Ny | 2 cfs | → |
| Sampawams Creek At Babylon Ny | 9 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Lefferts Grist Mill Dam.
Boat launches
- Lloyd Harbor Road 72, Lloyd Harbor
- Scudder Park
- Asharoken Avenue Asharoken
- Seagate Road 3, Greenwich
- Long Island Greenbelt Trail Suffolk County
Campgrounds
- Park Shore Day Camp
- Battle Row
- Blydenburgh Park
- Ward Pound Ridge Reservation
- Cathedral Pines County Park
- Watch Hill Campgrounds
Fishing spots
Track Lefferts Grist Mill Dam in the Snoflo app
Save this dam as a favorite and get the local NOAA / yr.no forecast plus regional flow context wherever you are.
About Lefferts Grist Mill Dam
Where does the data for Lefferts Grist Mill Dam come from?
Structural and regulatory data come from the U.S. Army Corps of Engineers' National Inventory of Dams (NID). Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
NID structural data refreshes annually as the Corps publishes updated assessments. The weather forecast refreshes throughout the day.
What does the Low hazard rating mean?
The Corps of Engineers' hazard potential classification grades probable consequences if the dam fails: High = probable loss of human life; Significant = no probable loss of human life but possible economic loss / environmental damage; Low = no probable loss of human life, only minor economic / environmental losses. See the Dam Data Reference card above for the full definitions.
What's "% of normal"?
The current storage value compared to the historical average storage on this calendar day. 100% = right on average; values above 100% mean above-normal storage (wet year); values below mean below-normal (dry year or drought).
Can I get alerts when storage crosses a threshold?
Yes -- alerts are managed in the Snoflo iOS app. Favorite this dam, set a threshold, and you'll get a push the moment conditions cross.
Other water bodies near here
Snoflo-tracked reservoirs and dams within driving distance of Lefferts Grist Mill Dam.