Zimmerman Retention Dam #1 Reservoir Report
Last Updated: December 5, 2025
Zimmerman Retention Dam #1, located in Mosby, Montana, is a gravity dam primarily used for fire protection, livestock, and as a small fish pond.
°F
°F
mph
Wind
%
Humidity
Summary
Built in 2003 by the Bureau of Land Management, this dam has a hydraulic height of 15 feet and a structural height of 19 feet, with a capacity to store up to 103 acre-feet of water. Situated on Flatwillow Creek in the Musselshell River basin, the dam covers a surface area of 20.29 acres and serves a drainage area of 0.7 square miles.
With a low hazard potential and a condition assessment of "Not Rated," Zimmerman Retention Dam #1 poses minimal risk to the surrounding area. Despite not being regulated by the state, the dam undergoes inspections every five years to ensure its structural integrity and safety. The dam does not have a spillway or outlet gates, indicating a simple design aimed at meeting its primary purposes efficiently.
Managed and funded by the Bureau of Land Management, Zimmerman Retention Dam #1 stands as a vital resource for water retention and fire protection in the region. Its strategic location and design make it a key asset in safeguarding the local ecosystem and supporting the agricultural activities in the area.
Year Completed |
2003 |
Dam Length |
179 |
River Or Stream |
FLATWILLOW CK./MUSSELSHELL RIV |
Primary Dam Type |
Gravity |
Surface Area |
20.29 |
Hydraulic Height |
15 |
Drainage Area |
0.7 |
Nid Storage |
103 |
Structural Height |
19 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
19 |
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.
Zimmerman Retention Dam #1