Oneill Forebay Reservoir Report

Last Updated: December 5, 2025

O'Neill Forebay is a man-made reservoir located in California's Central Valley.


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Summary

Its construction was completed in 1967 and it serves as a part of the State Water Project, which supplies water to various regions of California. The reservoir's primary source of water is the San Luis Reservoir, which is fed by surface water flows from the Sacramento-San Joaquin Delta and snowmelt from the Sierra Nevada Mountains. The reservoir also receives additional water from the California Aqueduct. O'Neill Forebay is used for agricultural irrigation and provides water to nearby farms. It is also a popular destination for recreational activities such as boating, fishing, and camping. The reservoir holds a capacity of 93,000 acre-feet of water and is operated by the California Department of Water Resources.

Reservoir Details

Storage 24hr Change -4.49%
Percent of Normal 92%
Minimum 36,527.0 acre-ft
2023-01-18
Maximum 54,212.0 acre-ft
2023-12-21
Average 49,189 acre-ft
       
Seasonal Comparison
Storage Levels
Pool Elevation Levels
Top Conserv Storage Levels
Inflow Levels

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.