Island Lake Dam Reservoir Report

Last Updated: December 5, 2025

Island Lake Dam, located in Island Lake, Illinois, on Cotton Creek, stands as a testament to the intersection of water resource management and recreational enjoyment.


°F

°F

mph

Wind

%

Humidity

Summary

Constructed in 1940, this earth dam with a height of 12 feet and a length of 160 feet serves primarily for recreational purposes, offering a storage capacity of 470 acre-feet. Managed by the local government and regulated by the Illinois Department of Natural Resources, the dam boasts a low hazard potential and a moderate risk assessment, ensuring the safety of nearby residents and visitors.

Despite its age, Island Lake Dam has undergone regular inspections, with the latest inspection taking place in July 2019. With a designated inspection frequency of 5 years, the dam's condition assessment is currently listed as "Not Available," indicating a need for further evaluation. While the dam's emergency action plan status is not specified, its spillway type is noted as "Uncontrolled" with a width of 18 feet. The dam's risk management measures and inundation maps preparation status are also unspecified, pointing to areas for potential improvement to enhance overall safety and preparedness.

In conclusion, Island Lake Dam serves not only as a recreational hotspot but also as a vital component of water resource management in McHenry County, Illinois. With its relatively low hazard potential and moderate risk assessment, continued monitoring and potential enhancements to its emergency preparedness measures could further ensure the safety and resilience of the surrounding community in the face of changing climate conditions.

Year Completed

1940

Dam Length

160

Dam Height

12

River Or Stream

COTTON CREEK

Primary Dam Type

Earth

Nid Storage

470

Outlet Gates

None

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

12
       
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.