Jocko Reservoir Report

Last Updated: December 5, 2025

Jocko is a federal-owned dam located in Missoula, Montana, with a primary purpose of irrigation.


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Summary

Built in 1937 by the Bureau of Indian Affairs, Jocko Dam stands at a structural height of 93 feet and has a storage capacity of 8,869 acre-feet. The dam spans 310 feet along the Jocko River and is primarily constructed from earth materials, serving as a vital resource for water management in the region.

Despite its age, Jocko Dam remains a crucial infrastructure for water supply and recreational activities in the area. With a high hazard potential, the dam is subject to regular inspections by the Bureau of Indian Affairs to ensure its safety and functionality. The dam's controlled spillway and historical significance make it a key feature in the landscape of Arlee, Montana, offering both practical benefits and a glimpse into the region's water resource management history.

With its very high risk assessment rating, Jocko Dam underscores the importance of effective risk management and emergency preparedness. Although the condition assessment is currently listed as "Not Available," the Bureau of Indian Affairs continues to monitor and maintain the dam to mitigate potential hazards and ensure the safety of surrounding communities. As a key player in the irrigation infrastructure of the area, Jocko Dam's role in water resource management and climate resilience highlights the need for ongoing vigilance and proactive measures to safeguard this essential resource.

Year Completed

1937

Dam Length

310

River Or Stream

JOCKO RIVER

Primary Dam Type

Earth

Nid Storage

8869

Structural Height

93

Hazard Potential

High

Nid Height

93
       
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.