Oso Largo Dam Reservoir Report
Nearby: Indian Farms Billingsley Dam
Last Updated: December 5, 2025
Oso Largo Dam, located in Fort Thomas, Arizona, along the Gila River, was completed in 1971 by the Bureau of Land Management with a primary purpose of flood risk reduction.
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Summary
This gravity dam stands at a structural height of 26 feet with a hydraulic height of 21 feet, offering a storage capacity of 616.7 acre-feet and serving a drainage area of 93.7 square miles. With a surface area of 241 acres, this dam plays a critical role in managing water resources in the region.
Despite its low hazard potential, Oso Largo Dam has been assessed as unsatisfactory in condition, warranting a closer inspection and potential maintenance to ensure its long-term functionality. The dam features an uncontrolled spillway with a width of 5 feet and has a moderate risk level assigned to it. While the dam has not been modified in recent years, regular inspections are carried out every five years to monitor its structural integrity and safety measures. With Oso Largo Dam being a key component for flood risk reduction in the area, its management and maintenance are essential for water resource and climate enthusiasts to monitor.
Year Completed |
1971 |
Dam Length |
4625 |
River Or Stream |
GILA RIVER |
Primary Dam Type |
Gravity |
Surface Area |
241 |
Hydraulic Height |
21 |
Drainage Area |
93.7 |
Nid Storage |
616.7 |
Structural Height |
26 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
26 |
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.
Oso Largo Dam