Conn Creek Reservoir Report

Last Updated: December 5, 2025

In the heart of Napa, California, lies Conn Creek, also known as Lake Hennessey, a water supply reservoir built in 1946 and managed by the local government.


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Summary

This Earth-type dam stands at 125 feet high and has a storage capacity of 31,000 acre-feet, serving primarily for irrigation and water supply purposes. With a surface area of 790 acres and a drainage area of 54 square miles, Conn Creek plays a vital role in supporting the agricultural and residential needs of the region.

Despite its age, Conn Creek has undergone regular state inspections and enforcement to ensure its safety and functionality. The dam's hazard potential is classified as high, but its condition assessment rates as fair, with the last inspection conducted in December 2020. Located in the picturesque city of Rutherford, this reservoir offers a serene escape for water resource and climate enthusiasts, showcasing the intersection of human ingenuity and natural beauty in water management.

As a key component of the Sacramento District, Conn Creek highlights the importance of sustainable water resource management in the face of climate change challenges. Its strategic location, coupled with its historical significance and ongoing regulatory oversight, underscores the critical role that dams like Conn Creek play in preserving and enhancing water security for communities in California. Explore Conn Creek to witness firsthand the harmonious blend of environmental stewardship and engineering excellence in water infrastructure.

Year Completed

1946

Dam Length

700

Dam Height

125

River Or Stream

Conn Creek

Primary Dam Type

Earth

Surface Area

790

Hydraulic Height

110

Drainage Area

54

Nid Storage

31000

Hazard Potential

High

Nid Height

125
       
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.