Deer Lake Reservoir Report

Last Updated: December 5, 2025

Deer Lake, located in Angwin, California, is a privately owned earth-type dam that was completed in 1958 for the primary purpose of water supply.


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Summary

With a dam height of 72 feet and a hydraulic height of 62.7 feet, Deer Lake has a storage capacity of 248 acre-feet and covers a surface area of 10 acres. The dam sits on Tr Angwin Creek and is regulated by the California Department of Water Resources (DWR) for safety and inspection.

Despite its small size in terms of storage and drainage area, Deer Lake poses a high hazard potential and is subject to regular inspections to ensure its structural integrity. The dam's condition assessment in 2017 deemed it satisfactory, and emergency action plans are in place to mitigate potential risks. The surrounding area offers opportunities for irrigation, recreation, and of course, water supply, making Deer Lake an important resource in the region for both residents and wildlife alike.

With its picturesque location in Napa County, Deer Lake serves as a vital water source for the community of Angwin and beyond. As climate change continues to impact water resources, the maintenance and regulation of dams like Deer Lake become increasingly crucial for ensuring a sustainable water supply for future generations. As enthusiasts of water resources and climate conservation, it is essential to monitor and support efforts to safeguard and enhance the resilience of dams like Deer Lake in the face of changing environmental conditions.

Year Completed

1958

Dam Length

620

Dam Height

72

River Or Stream

Tr Angwin Creek

Primary Dam Type

Earth

Surface Area

10

Hydraulic Height

62.7

Drainage Area

0.22

Nid Storage

248

Hazard Potential

High

Nid Height

72
       
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.