Holly Oaks Lake Dam Reservoir Report

Last Updated: December 5, 2025

Holly Oaks Lake Dam, located in Jacksonville, Florida, serves multiple purposes including flood risk reduction, recreation, and water supply.


°F

°F

mph

Wind

%

Humidity

Summary

This private dam is regulated by the Florida Department of Environmental Protection and has a significant hazard potential with a fair condition assessment. The dam stands at a height of 6 feet with a hydraulic height of 4 feet and a length of 495 feet, holding a maximum storage capacity of 64 acre-feet and a normal storage of 51 acre-feet.

Situated on the Mill Cove-St. Johns river/stream, Holly Oaks Lake Dam's spillway is uncontrolled with a width of 6 feet. Although the dam has a moderate risk assessment rating of 3, it has not been modified in recent years and lacks outlet gates. The last inspection in May 2017 deemed the dam to be in fair condition, highlighting the importance of regular monitoring and maintenance to ensure the safety and integrity of this vital water resource structure in Duval County, Florida.

Enthusiasts of water resources and climate will find Holly Oaks Lake Dam to be a fascinating case study in dam engineering and management. With its diverse purposes, significant hazard potential, and unique design features, this private earth dam presents a complex yet critical piece of infrastructure in the flood-prone region of Jacksonville. As climate change continues to impact water resources, the maintenance and regulation of structures like Holly Oaks Lake Dam become increasingly important to mitigate risks and ensure the sustainable utilization of water for the community.

Dam Length

495

Dam Height

6

River Or Stream

MILL COVE-ST. JOHNS

Primary Dam Type

Earth

Surface Area

24

Hydraulic Height

4

Drainage Area

1.96

Nid Storage

64

Outlet Gates

None

Hazard Potential

Significant

Foundations

Rock, Soil

Nid Height

6
       
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.