American Zinc Smelter Company Large Lake Dam Reservoir Report
Last Updated: December 6, 2025
The American Zinc Smelter Company Large Lake Dam, located in Hillsboro, Illinois, is a privately owned structure that serves the primary purpose of water supply.
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Summary
Built in 1916, this Earth dam stands at a height of 31 feet and has a length of 320 feet, with a storage capacity of 300 acre-feet. The dam is situated on the Middle Fork Shoal Creek and is regulated by the Illinois Department of Natural Resources.
Despite its low hazard potential, the dam is classified as having a moderate risk level, with an inspection frequency of 5 years. The dam features an uncontrolled spillway and outlet gates, with a spillway width of 12 feet. While the condition assessment is currently not available, the dam is regularly inspected to ensure its safety and functionality. Overall, the American Zinc Smelter Company Large Lake Dam is a significant water resource infrastructure in the region, contributing to water supply needs and serving as a vital component of the local ecosystem.
Year Completed |
1916 |
Dam Length |
320 |
Dam Height |
31 |
River Or Stream |
MIDDLE FORK SHOAL CREEK |
Primary Dam Type |
Earth |
Nid Storage |
300 |
Outlet Gates |
Uncontrolled |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
31 |
Seasonal Comparison
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Nearby Streamflow Levels
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.
American Zinc Smelter Company Large Lake Dam