San Lorenzo Creek Reservoir Report

Last Updated: December 5, 2025

San Lorenzo Creek, also known as Don Castro Reservoir, is a vital water resource located in Castro Valley, California.


°F

°F

mph

Wind

%

Humidity

Summary

Managed by the local government, this dam serves primarily for flood risk reduction and recreation purposes. Constructed in 1964, this earth dam stands at a height of 65 feet and has a storage capacity of 380 acre-feet, covering a surface area of 24 acres.

With a high hazard potential but assessed as satisfactory in condition, San Lorenzo Creek plays a crucial role in managing the region's water resources. The dam is regulated by the California Department of Water Resources and undergoes regular inspections to ensure its safety and reliability. Despite its age, the dam continues to provide flood protection and recreational opportunities for the local community.

San Lorenzo Creek's importance extends beyond flood risk reduction, serving as a significant water infrastructure in Alameda County. As climate change poses increasing challenges to water resources management, this dam remains a key asset in safeguarding against potential disasters and ensuring sustainable water use for the future. With its strategic location and vital role in the region, San Lorenzo Creek stands as a testament to the ongoing efforts to balance water resource management with environmental conservation and public safety.

Year Completed

1964

Dam Length

385

Dam Height

65

River Or Stream

San Lorenzo Creek

Primary Dam Type

Earth

Surface Area

24

Hydraulic Height

50

Drainage Area

19.9

Nid Storage

380

Hazard Potential

High

Nid Height

65
       
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.