Millsboro Pond Dam Reservoir Report

Last Updated: December 5, 2025

Millsboro Pond Dam, located in Sussex County, Delaware, is a gravity dam completed in 1920 with a primary purpose of creating a fish and wildlife pond.


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Summary

The dam stands at a height of 15.13 feet and has a length of 510 feet, impounding a maximum storage of 336 acre-feet. The dam is situated on Mirey Branch, with a drainage area of 62.4 square miles and a surface area of 183.65 acres.

Despite its historical significance, Millsboro Pond Dam is currently rated as having a high hazard potential and poor condition assessment. The last inspection in April 2020 revealed the need for improvements, with a very high risk assessment rating. The dam is regulated by the Delaware Department of Natural Resources and Environmental Control (DNREC), with state permitting, inspection, and enforcement in place to ensure public safety and environmental protection.

The presence of two slide gates for outlet control and a controlled spillway with a width of 160 feet indicate the importance of proper maintenance and monitoring of Millsboro Pond Dam. With its critical role in providing habitat for fish and wildlife, as well as recreational opportunities, efforts to address the dam's condition and reduce risk are essential for the long-term safety and sustainability of this water resource in Delaware.

Year Completed

1920

Dam Length

510

Dam Height

15.13

River Or Stream

MIREY BRANCH

Primary Dam Type

Gravity

Surface Area

183.65

Drainage Area

62.4

Nid Storage

336

Outlet Gates

Slide (sluice gate) - 2

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

15
       
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.