Mammoth Lake Reservoir Report

Last Updated: December 5, 2025

Mammoth Lake, located in Mount Pleasant Township, Pennsylvania, is a picturesque earth dam structure built in 1969 primarily for recreational purposes.


°F

°F

mph

Wind

%

Humidity

Summary

With a height of 15 feet and a length of 1100 feet, this dam has a storage capacity of 342 acre-feet, making it a popular destination for outdoor enthusiasts in the Westmoreland County area. The lake covers a surface area of 27 acres and is fed by Wetley Run, providing a tranquil environment for fishing, boating, and other water-related activities.

Owned and regulated by the Pennsylvania Department of Environmental Protection, Mammoth Lake is regularly inspected to ensure its structural integrity and safety. Despite its high hazard potential, the dam's condition is deemed satisfactory, with a hazard potential rating of "High." The last inspection in August 2019 confirmed its soundness, reassuring visitors of its reliability for continued recreational use. As water resource and climate enthusiasts, you will appreciate the efforts taken to maintain this important water body for both enjoyment and environmental conservation in the region.

Mammoth Lake stands as a testament to the careful management of water resources in Pennsylvania, offering a serene retreat for locals and visitors alike. Its scenic beauty, combined with its essential role in providing recreational opportunities, highlights the importance of preserving and protecting our natural water sources. Whether you are interested in the engineering behind its construction or simply looking for a peaceful escape in nature, Mammoth Lake is sure to captivate water resource and climate enthusiasts with its blend of utility and charm.

Year Completed

1969

Dam Length

1100

Dam Height

15

River Or Stream

WETLEY RUN

Primary Dam Type

Earth

Surface Area

27

Drainage Area

8.5

Nid Storage

342

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

15
       
Seasonal Comparison

Weather Forecast

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. 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

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, 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.