South Lake Dam Reservoir Report

Last Updated: December 13, 2025

South Lake Dam, located in Huntley-Offstream, Illinois, is a privately-owned structure with a primary purpose of recreation.


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Summary

Built in 1965 by designer E. C. Bowen, Jr., this earth dam stands at a height of 16 feet and stretches 500 feet in length, providing a storage capacity of 119 acre-feet. The dam is regulated by the Illinois Department of Natural Resources, with state permitting, inspection, and enforcement in place to ensure its safety and compliance.

With a low hazard potential and a moderate risk assessment rating, South Lake Dam is considered a relatively safe structure. Its spillway, of uncontrolled type with a width of 30 feet, helps manage water flow in the event of excess storage. Although the condition assessment is not available, regular inspections are conducted every five years to monitor the dam's integrity. Despite its private ownership, the dam plays a crucial role in providing recreational opportunities and water resource management in the McHenry County area.

South Lake Dam is not only a recreational spot but also a vital piece of infrastructure in the South Branch Kishwaukee River watershed. With its historical significance dating back to the 1960s, this earthen dam serves as a reminder of the importance of sustainable water resource management in the face of changing climate patterns. As climate enthusiasts, understanding and advocating for the safety and maintenance of structures like South Lake Dam is essential for ensuring the resilience of our water systems in the future.

Year Completed

1965

Dam Length

500

Dam Height

16

River Or Stream

TRIB SOUTH BRANCH KISHWAUKEE RIVER

Primary Dam Type

Earth

Nid Storage

119

Outlet Gates

None

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

16
       
Seasonal Comparison

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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.