Gem Lake Reservoir Report

Last Updated: December 5, 2025

Gem Lake, located in Mono County, California, is a private hydroelectric dam constructed in 1917 by L.R.


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Summary

Jorgensen. The dam stands at a height of 80 feet and has a capacity of 17,228 acre-feet, serving as a vital source of water storage for the surrounding area. With a maximum discharge of 1,700 cubic feet per second, Gem Lake plays a crucial role in regulating water flow and providing hydroelectric power to the region.

The dam's primary purpose is hydroelectric generation, but it also offers recreational opportunities for visitors to enjoy. Situated on Rush Creek, the dam spans 688 feet in length and covers a surface area of 282 acres. Despite its age, Gem Lake Dam is regularly inspected and regulated by both state and federal agencies to ensure its structural integrity and safety. With a high hazard potential and moderate risk assessment, the dam remains a key feature in the water resource management and climate resilience efforts in the area.

Gem Lake Dam is a testament to the intersection of human ingenuity and natural resource management, showcasing the importance of sustainable hydroelectric infrastructure in a changing climate. As water resource and climate enthusiasts, understanding the significance of structures like Gem Lake Dam is crucial in safeguarding our water supply and adapting to environmental challenges. With its rich history and continued utility, Gem Lake Dam stands as a symbol of resilience and innovation in the face of evolving climate conditions.

Year Completed

1917

Dam Length

688

Dam Height

80

River Or Stream

Rush Creek

Primary Dam Type

Concrete

Surface Area

282

Hydraulic Height

80

Drainage Area

21.6

Nid Storage

17228

Structural Height

80

Hazard Potential

High

Foundations

Rock

Nid Height

80
       
Seasonal Comparison

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.