J.L. Big Reservoir Reservoir Report
Nearby: Reagan Lake Upsilon
Last Updated: January 11, 2026
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Summary
Big Reservoir, located in Glacier County, Montana, is a privately owned water storage structure primarily used for irrigation purposes along Sage Creek. The reservoir has a storage capacity of 342 acre-feet and covers a surface area of 59 acres. The dam, which stands at a height of 23.5 feet, has a low hazard potential and is currently not rated in terms of condition assessment.
Managed by the Montana Department of Natural Resources and Conservation (DNRC), J.L. Big Reservoir is regulated, permitted, inspected, and enforced by the state agency. The reservoir's emergency action plan (EAP) status, risk assessment, and risk management measures are currently not available, indicating a potential need for further evaluation and updates to ensure its safety and functionality. Despite its low hazard potential, the reservoir serves as a crucial water resource for irrigation in the region, highlighting the importance of proper maintenance and oversight to sustain its operations effectively.
Dam Height |
23.5 |
River Or Stream |
SAGE CREEK |
Primary Dam Type |
Earth |
Surface Area |
59 |
Hydraulic Height |
14.5 |
Nid Storage |
342 |
Hazard Potential |
Low |
Nid Height |
24 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
J.L. Big Reservoir