West Fork Bitterroot (Painted Rocks) Reservoir Report

Reservoir Report

Montana

Last Updated: December 5, 2025

West Fork Bitterroot (Painted Rocks) is a state-owned dam located in Ravalli, Montana, along the West Fork of the Bitterroot River.

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Summary

Completed in 1940, this earth dam stands at a height of 143 feet and serves primarily for irrigation purposes, with a storage capacity of 45,100 acre-feet. Despite its age, the dam has a high hazard potential and is currently rated as in poor condition, requiring regular inspections and maintenance to ensure its safety and functionality.

The dam's spillway, with a width of 160 feet, is uncontrolled, and it has a maximum discharge capacity of 3,300 cubic feet per second. The surrounding area covers 655 acres, with a drainage area of 316 square miles. The dam's reservoir has a normal storage capacity of 31,706 acre-feet, providing vital water resources for agricultural irrigation in the region. The dam is under the regulatory oversight of the Montana Department of Natural Resources and Conservation (DNRC), with state permitting, inspection, and enforcement in place to ensure compliance with safety standards.

With its historical significance and critical role in water resource management for irrigation, West Fork Bitterroot (Painted Rocks) serves as a key infrastructure in the region. As climate change impacts water availability and quality, the maintenance and upkeep of this dam become increasingly important to ensure the sustainable use of water resources for agriculture and other essential purposes. Ongoing risk assessments and management measures are necessary to address the dam's high hazard potential and poor condition, highlighting the importance of proactive measures to safeguard this vital piece of infrastructure for the future.

Year Completed	1940
Dam Length	800
Dam Height	143
River Or Stream	WEST FORK OF BITTERROOT
Primary Dam Type	Earth
Surface Area	655
Hydraulic Height	143
Drainage Area	316
Nid Storage	45100
Hazard Potential	High
Foundations	Rock
Nid Height	143

Explore Interactive Map

WEST FORK BITTERROOT (PAINTED ROCKS)

Reservoir Report • Water Levels • Weather Forecast

December 5, 2025

Year_Completed	1940
Dam_Length	800
Dam_Height	143
River_Or_Stream	WEST FORK OF BITTERROOT
Primary_Dam_Type	Earth
Surface_Area	655
Hydraulic_Height	143
Drainage_Area	316
Nid_Storage	45100
Hazard_Potential	High
Foundations	Rock
Nid_Height	143

Seasonal Comparison

Weather Forecast

Nearby Streamflow Levels

West Fork Bitterroot River Nr Conner Mt 52.8cfs	53cfs
Bitterroot River Near Darby Mt 247.0cfs	247cfs
Salmon River Nr Shoup Id 1550.0cfs	1550cfs
Middle Fork Salmon River At Mouth Nr Shoup Id 1020.0cfs	1020cfs
Napias Creek Below Arnett Creek Near Leesburg 9.65cfs	10cfs
Big Hole River Bl Big Lake Cr At Wisdom Mt 80.9cfs	81cfs

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.