Lower Twin Lake Reservoir Report

Last Updated: December 5, 2025

Lower Twin Lake, located in Mono County, California, is a private water supply dam with a history dating back to its completion in 1888.


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Summary

The dam, primarily serving irrigation and water supply purposes, stands at a height of 16 feet with a hydraulic height of 11.7 feet. It stores a maximum capacity of 4011 acre-feet of water and covers a surface area of 399 acres, drawing from a drainage area of 39.1 square miles.

Managed by the California Department of Water Resources (DWR) and regulated for safety by the Safety of Dams agency, Lower Twin Lake's dam has a high hazard potential but is currently rated in fair condition as of the last assessment in September 2017. The dam's emergency action plan was last revised in August 2019, ensuring preparedness in the event of a crisis. With a recent inspection in October 2020 and a regular inspection frequency of 1 year, the dam remains under careful monitoring to ensure its structural integrity and continued safe operation.

Surrounded by the stunning scenery of Bridgeport and fed by Robinson Creek, Lower Twin Lake stands as a vital resource for water supply and agricultural irrigation in the region. Its historical significance, coupled with its ongoing regulatory oversight and maintenance efforts, highlights the importance of sustainable water management practices in the face of changing climate conditions. Enthusiasts of water resources and climate resilience can appreciate the role that Lower Twin Lake plays in balancing human needs with environmental stewardship in California's diverse landscape.

Year Completed

1888

Dam Length

240

Dam Height

16

River Or Stream

Robinson Creek

Primary Dam Type

Earth

Surface Area

399

Hydraulic Height

11.7

Drainage Area

39.1

Nid Storage

4011

Hazard Potential

High

Nid Height

16
       
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.