San Andreas Reservoir Report

Last Updated: December 5, 2025

San Andreas, also known as San Andreas Lake, is a significant water resource located in San Mateo, California.


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Summary

Owned by the local government, this dam serves as a vital water supply infrastructure, completed in 1870 and standing at a height of 107 feet. With a storage capacity of 19,027 acre-feet and a surface area of 550 acres, San Andreas plays a crucial role in providing water to the surrounding area.

Managed and regulated by the California Department of Water Resources (DWR) and Safety of Dams, San Andreas is subject to regular inspections to ensure its safety and maintenance. Despite being classified as having a high hazard potential, the dam is currently in fair condition. The last inspection in December 2020 revealed its compliance with safety standards, with an emergency action plan in place and regular assessments of its risk management measures. With its location on Tr San Mateo Cr and its proximity to the city of San Mateo, San Andreas is a key player in the water infrastructure of the region.

Enthusiasts of water resources and climate will find San Andreas to be a fascinating case study in dam management and water supply infrastructure. With its historical significance, structural design, and regulatory oversight, this dam exemplifies the complex interplay between human engineering and natural resources. As one of the critical elements in California's water supply system, San Andreas stands as a testament to the ongoing efforts to balance water management, safety regulations, and environmental sustainability in the face of changing climate conditions.

Year Completed

1870

Dam Length

727

Dam Height

107

River Or Stream

Tr San Mateo Cr

Primary Dam Type

Earth

Surface Area

550

Hydraulic Height

97

Drainage Area

4.4

Nid Storage

19027

Hazard Potential

High

Nid Height

107
       
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.