Mammoth Pool Reservoir Report

Last Updated: December 5, 2025

Mammoth Pool is a reservoir located in the Sierra National Forest of California.


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Summary

The history of the reservoir dates back to the early 1900s, when it was constructed as part of the San Joaquin Electric Company's hydroelectric system. The reservoir is fed by several creeks and streams, including the San Joaquin River, as well as snowpack melt from the surrounding mountains. The hydrology of the area is complex and includes a network of aqueducts and pipelines that deliver water to agricultural and urban areas in the Central Valley. The surface flow from Mammoth Pool is used for irrigation in the Fresno area, while the snowpack provides important water resources for the state. The reservoir is also a popular recreational destination, with opportunities for fishing, boating, and camping.

Reservoir Details

Storage 24hr Change None%
Percent of Normal None%
Minimum 10,916.0 acre-ft
2021-10-05
Maximum 128,184.0 acre-ft
2023-06-06
Average acre-ft
Dam_Height 411
Hydraulic_Height 330
Drainage_Area 995
Year_Completed 1960
Nid_Storage 122175
Structural_Height 411
River_Or_Stream San Joaquin River
Foundations Rock
Surface_Area 1100
Hazard_Potential High
Dam_Length 820
Primary_Dam_Type Earth
Nid_Height 411
       
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.