Williston Mill Dam (Md 617 Old Harmony Road) Reservoir Report
Nearby: Scull Farm Pond Nagels Mill Pond
Last Updated: December 5, 2025
Located in Williston, Maryland, the Williston Mill Dam, also known as Todds Mill Pond, is a privately owned structure that serves primarily for recreation purposes.
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Summary
Constructed in 1936, this earth dam stands at a height of 18 feet and spans a length of 630 feet along Mill Creek. With a storage capacity of 585 acre-feet, this dam plays a role in regulating the flow of water and providing a surface area of 51.6 acres for recreational activities.
Managed by the Maryland Dam Safety agency, the Williston Mill Dam has a low hazard potential and is currently rated as "Not Rated" in terms of condition assessment. Despite its relatively low risk level, the dam is subject to regular state inspections and enforcement to ensure its safety and functionality for the surrounding community. With a maximum discharge capacity of 1660 cubic feet per second and a controlled spillway design, the dam is equipped to handle potential excess water flow in a controlled manner.
While the Williston Mill Dam may not pose a significant risk currently, its location within a high-risk area highlights the importance of ongoing risk management measures. With a very high risk assessment score of 1, it is crucial for the dam owners and regulatory agencies to continue monitoring and maintaining the structure to prevent any potential incidents or emergencies. For water resource and climate enthusiasts, the Williston Mill Dam serves as a fascinating example of how human-made structures can both enhance recreational opportunities and play a crucial role in water management within local ecosystems.
Year Completed |
1936 |
Dam Length |
630 |
Dam Height |
18 |
River Or Stream |
Mill Creek |
Primary Dam Type |
Earth |
Surface Area |
51.6 |
Drainage Area |
7.9 |
Nid Storage |
585 |
Outlet Gates |
Slide (sluice gate) - 0 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
18 |
Seasonal Comparison
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Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Williston Mill Dam (Md 617 Old Harmony Road)