Gem Lake Reservoir Report

Last Updated: December 5, 2025

Gem Lake is a small, high-altitude body of water located in the Sierra Nevada Mountains of California, near Mammoth Lakes.


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Summary

The lake was formed by glacial activity during the last Ice Age, and is fed by several snowmelt streams and small springs. The surrounding area is home to a variety of wildlife, including black bears, mule deer, and mountain lions. There are several hiking trails leading to and around the lake, making it a popular destination for outdoor enthusiasts. The area is also used for recreational activities such as fishing and camping. In addition, the water from Gem Lake is used for irrigation purposes by nearby agricultural operations.

Reservoir Details

24hr Change None%
Percent of Normal None%
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Average
Nid_Height 80
Hydraulic_Height 80
Drainage_Area 21.6
Year_Completed 1917
Dam_Height 80
Hazard_Potential High
Structural_Height 80
Primary_Dam_Type Concrete
River_Or_Stream Rush Creek
Foundations Rock
Surface_Area 282
Nid_Storage 17228
Dam_Length 688
       
Seasonal Comparison
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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.