Lake Mahopac Dam
Lake Mahopac Dam is an earth dam located in Putnam County, New York, built in 1940. It carries a Significant hazard potential classification and has a satisfactory condition assessment.
About Lake Mahopac Dam
The primary purpose of Lake Mahopac Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Town Of Carmel (local government). It impounds the Muscoot River near Mahopac Falls.
The dam stands 9 feet tall and stretches 190 feet across, creates a reservoir covering 583 acres, has a maximum storage capacity of 17,850 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1940, the structure is well-established, with more than 75 years of service.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 03/17/2025.
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Location
| State | New York |
| County | Putnam |
| Nearest City | Mahopac Falls |
| River/Stream | Muscoot River |
| Coordinates | 41.37417, -73.75417 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 9 ft |
| Dam Height | 9 ft |
| Dam Length | 190 ft |
| Year Completed | 1940 (86 years old) |
Storage & Hydraulics
| NID Storage | 17,850 acre-ft |
| Max Storage | 17,850 acre-ft |
| Normal Storage | 16,684 acre-ft |
| Surface Area | 583 acres |
| Drainage Area | 1 sq mi |
| Max Discharge | 109 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | TOWN OF CARMEL |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Satisfactory |
| Last Inspection | 03/17/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | NY01329 |
| Federal ID | NY01329 |
| More Info | State Dam Safety Program |