Big Mac #1 Reservoir Report
Nearby: Happy Jack #1 John Boy #2
Last Updated: December 6, 2025
Big Mac #1, also known as Mike's Milkshake, is a privately owned earth dam located in Garfield, Montana, along TR-Big Dry Creek.
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Summary
Built in 1947 by the USDA NRCS, this dam serves multiple purposes including fire protection, stock watering, and creating a small fish pond. With a height of 35 feet and a length of 500 feet, the dam has a storage capacity of 157 acre-feet and covers a drainage area of 3.13 square miles.
Managed by the Montana Department of Natural Resources and Conservation (DNRC), Big Mac #1 is classified as a low hazard potential structure. Despite not being rated for its condition, the dam is regularly inspected, permitted, and enforced by the state regulatory agency. The spillway width of 250 feet ensures proper water release during periods of high flow, further minimizing any potential risks associated with the structure. While the dam's emergency action plan status is not specified, its strategic location and design provide essential water resource management benefits for the surrounding area.
Year Completed |
1947 |
Dam Length |
500 |
Dam Height |
35 |
River Or Stream |
TR-BIG DRY CREEK |
Primary Dam Type |
Earth |
Hydraulic Height |
35 |
Drainage Area |
3.13 |
Nid Storage |
157 |
Hazard Potential |
Low |
Nid Height |
35 |
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.
Big Mac #1