Decock #3 Reservoir Report
Nearby: Froze-To-Death #3 Froze-To-Death #4
Last Updated: December 8, 2025
Decock #3 is a privately owned earth dam located in Hysham, Montana, along the TR-Yellowstone River.
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Summary
Constructed in 1949 by the USDA NRCS, this dam serves multiple purposes including fire protection, stock, and small fish pond. With a height of 15 feet and a length of 250 feet, Decock #3 has a storage capacity of 193 acre-feet and a drainage area of 4.69 square miles.
Despite being classified as a low hazard potential structure, Decock #3 is regulated by the state of Montana and is subject to regular inspections and enforcement by the DNRC. The spillway of this dam is uncontrolled and measures 12 feet in width, with a maximum discharge of 160 cubic feet per second. While the condition assessment of Decock #3 is currently listed as "Not Rated," the risk assessment for this structure is moderate (3), indicating a level of risk that warrants attention and potential mitigation measures in the future.
Water resource and climate enthusiasts will appreciate the data on Decock #3, as it provides valuable insights into the infrastructure that plays a crucial role in managing water resources and protecting against various hazards in the region. With its unique design and multi-purpose functionality, Decock #3 serves as a testament to the importance of sustainable water management practices in maintaining the resilience of communities and ecosystems in Montana. The information on this dam serves as a reminder of the ongoing efforts to ensure the safety and effectiveness of water infrastructure in the face of changing climate conditions and evolving regulatory requirements.
Year Completed |
1949 |
Dam Length |
250 |
Dam Height |
15 |
River Or Stream |
TR-YELLOWSTONE RIVER |
Primary Dam Type |
Earth |
Hydraulic Height |
15 |
Drainage Area |
4.69 |
Nid Storage |
193 |
Hazard Potential |
Low |
Nid Height |
15 |
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.
Decock #3