Mammoth Lake
Mammoth Lake is an earth dam located in Westmoreland County, Pennsylvania, built in 1969. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Mammoth Lake
The primary purpose of Mammoth Lake is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Westmoreland County Commissioners (local government). It impounds the Wetley Run.
The dam stands 15 feet tall and stretches 1,100 feet across, creates a reservoir covering 27 acres, has a maximum storage capacity of 342 acre-feet, and collects water from a drainage area of 8 square miles. Completed in 1969, the structure is well into its service life at over 50 years old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. 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 08/12/2019.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Pennsylvania dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Pennsylvania |
| County | Westmoreland |
| River/Stream | Wetley Run |
| Coordinates | 40.21278, -79.45833 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 15 ft |
| Dam Height | 15 ft |
| Dam Length | 1,100 ft |
| Year Completed | 1969 (57 years old) |
Storage & Hydraulics
| NID Storage | 342 acre-ft |
| Max Storage | 342 acre-ft |
| Normal Storage | 182 acre-ft |
| Surface Area | 27 acres |
| Drainage Area | 8 sq mi |
Ownership & Safety
| Purpose | Recreation |
| Owner | WESTMORELAND COUNTY COMMISSIONERS |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 08/12/2019 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | PA00466 |
| Federal ID | PA00466 |
| More Info | State Dam Safety Program |