Thirtymile Reservoir Reservoir Report
Last Updated: December 6, 2025
Thirtymile Reservoir, located in Blaine, Montana, is a private irrigation reservoir built in 1933 on Thirtymile Creek.
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Summary
With a dam height of 14 feet and a capacity of 55 acre-feet, the reservoir serves as a crucial water source for agricultural irrigation in the region. The reservoir's primary purpose is irrigation, making it a vital resource for local farmers and landowners.
Managed by the Montana Department of Natural Resources & Conservation (DNRC), Thirtymile Reservoir has a low hazard potential and is currently rated as "Not Rated" in terms of condition assessment. Although the reservoir has not been modified in recent years, it continues to play a key role in water resource management and climate adaptation efforts in the area. With its gravity dam type and state-regulated status, Thirtymile Reservoir remains a significant water infrastructure asset in Montana.
Situated in a picturesque location near Savoy, Thirtymile Reservoir is an essential component of the local water supply infrastructure. Despite its relatively small size, the reservoir's strategic location and reliable water storage capacity make it a valuable asset for ensuring water security and supporting agricultural activities in the region. As climate change continues to impact water resources, Thirtymile Reservoir stands as a resilient and essential resource for water management and climate adaptation in Montana.
Year Completed |
1933 |
Dam Length |
40 |
Dam Height |
14 |
River Or Stream |
THIRTYMILE CREEK |
Primary Dam Type |
Gravity |
Hydraulic Height |
14 |
Nid Storage |
55 |
Hazard Potential |
Low |
Nid Height |
14 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Milk River Near Harlem Mt
|
69cfs |
Peoples Creek Near Hays Mt
|
4cfs |
Milk River Near Dodson Mt
|
68cfs |
Battle Creek Near Chinook Mt
|
12cfs |
Clear Creek Near Chinook Mt
|
21cfs |
Milk River At Malta Mt
|
0cfs |
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.
Thirtymile Reservoir