Herrin Lake Reservoir Report

Last Updated: December 5, 2025

Herrin Lake, located in Lewis and Clark County, Montana, is a state-regulated water resource with a primary purpose of serving as a fire protection, stock, or small fish pond.


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Summary

The dam, completed in 1949, is of earth type and stands at a height of 15 feet, with a storage capacity of 69 acre-feet. Despite its low hazard potential, the condition of Herrin Lake has not been rated, and there is no recent inspection data available.

This picturesque lake, situated in the Cottonwood area and fed by TR-WILLOW CREEK, provides essential water storage for the region, with a normal storage capacity of 36 acre-feet. While the dam has not been modified in recent years, it continues to play a vital role in maintaining water resources and supporting local ecosystems. As a water resource and climate enthusiast, Herrin Lake offers an opportunity to explore the intersection of human infrastructure and natural ecosystems in a stunning Montana setting.

With its serene waters and important role in fire protection and wildlife support, Herrin Lake is a valuable asset to the community. Managed by the Montana Department of Natural Resources and Conservation (DNRC), this dam exemplifies responsible water resource management in the region. As a visitor or researcher interested in water resources and climate, Herrin Lake offers a unique opportunity to study the impact of human intervention on natural water systems and the importance of sustainable practices for future generations.

Year Completed

1949

Dam Length

100

Dam Height

15

River Or Stream

TR-WILLOW CREEK

Primary Dam Type

Earth

Hydraulic Height

15

Nid Storage

69

Hazard Potential

Low

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.