Mahon Reservoir Reservoir Report
Last Updated: December 13, 2025
Mahon Reservoir, located in Harney County, Oregon, serves as a vital irrigation source for the surrounding area.
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Summary
Built in 1904, this Earth dam stands at a height of 25 feet and has a storage capacity of 3456 acre-feet. The reservoir is fed by Camp Creek and the South Fork Malheur River, with a drainage area of 30.4 square miles and a surface area of 12.1 acres.
With a low hazard potential and a moderate risk assessment rating, Mahon Reservoir is crucial for agricultural activities in the region. The dam has not been rated for its condition, but it is regularly inspected and maintained by the Oregon Water Resources Department. The spillway type is listed as uncontrolled, with a maximum discharge capacity of 90 cubic feet per second.
Despite its age, Mahon Reservoir continues to play a key role in water resource management in the area, providing reliable irrigation water for agricultural purposes. As a privately owned structure, it is subject to state regulations and inspections to ensure its safety and functionality. With its strategic location and historical significance, Mahon Reservoir stands as a testament to the importance of sustainable water management practices in the face of changing climate patterns.
Year Completed |
1904 |
Dam Length |
1200 |
Dam Height |
25 |
River Or Stream |
CAMP CREEK & SOUTH FORK MALHEUR RIVER |
Primary Dam Type |
Earth |
Surface Area |
12.1 |
Hydraulic Height |
23 |
Drainage Area |
30.4 |
Nid Storage |
3456 |
Structural Height |
31 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
31 |
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.
Mahon Reservoir