Marsh Lake Reservoir Report

Last Updated: December 5, 2025

Marsh Lake, also known as Mason Lake, is a private reservoir located in Pony, Montana, within the Cataract Creek watershed.


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Summary

Managed by the USDA NRCS, this irrigation dam was completed in 1956 and stands at a height of 8 feet with a length of 314 feet. The reservoir has a storage capacity of 68 acre-feet, primarily used for agricultural purposes in the surrounding area.

Despite its low hazard potential, Marsh Lake plays a crucial role in water resource management in the region, providing a reliable water source for irrigation. The dam is primarily composed of earth materials and is regulated by the Forest Service. With a maximum discharge of 54 cubic feet per second, the reservoir serves as a vital resource for maintaining water supply and supporting agricultural activities in Madison County, Montana.

As a key infrastructure for water management, Marsh Lake serves as a testament to the importance of sustainable water resource practices in the face of changing climate conditions. With its historical significance and ongoing role in supporting local agriculture, this private reservoir in Pony stands as a valuable asset in the region's water management efforts.

Year Completed

1956

Dam Length

314

Dam Height

8

River Or Stream

Cataract Creek

Primary Dam Type

Earth

Hydraulic Height

8

Nid Storage

68

Hazard Potential

Low

Nid Height

8
       
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.