Mcswain Reservoir Report

Last Updated: December 5, 2025

Mcswain, a hydroelectric dam located in Mariposa, California, is a public utility owned and regulated by the state of California.


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Summary

Completed in 1966, this rockfill dam stands at a height of 97 feet and has a maximum storage capacity of 9730 acre-feet. With its primary purpose being hydroelectric power generation, Mcswain also serves irrigation and recreation purposes, making it a versatile water resource in the region.

Managed by the Federal Energy Regulatory Commission, Mcswain boasts a spillway width of 625 feet and a maximum discharge capacity of 250,000 cubic feet per second. Its hazard potential is classified as high, with a moderate risk assessment score of 3. Despite its condition assessment being labeled as not available, the dam is regularly inspected, with the last inspection conducted in September 2020. The emergency action plan for Mcswain was last revised in January 2021, ensuring that necessary measures are in place to mitigate any potential risks associated with the dam.

In the picturesque setting along the Merced River, Mcswain not only provides essential water resources but also contributes to the local economy and recreational activities. With its strategic location and robust infrastructure, this dam continues to play a vital role in water management and power generation in the region, while adhering to strict regulatory standards set by state and federal agencies.

Year Completed

1966

Dam Length

1620

Dam Height

97

River Or Stream

Merced River

Primary Dam Type

Rockfill

Surface Area

310

Hydraulic Height

50

Drainage Area

1054

Nid Storage

9730

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

97
       
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.