Lewis Dam Reservoir Report

Last Updated: December 19, 2025

Lewis Dam, located in McDonough, Illinois, is a private earth dam with a primary purpose of recreation.


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Summary

It stands at a height of 28 feet and spans a length of 490 feet, holding a maximum storage capacity of 133.5 acre-feet. The dam overlooks the TRIB FARMERS FORK stream and is regulated by the Illinois Department of Natural Resources, with state permitting, inspection, and enforcement in place to ensure its safety and functionality.

While Lewis Dam poses a low hazard potential, it is equipped with an uncontrolled spillway with a width of 32 feet to manage maximum discharges of up to 355 cubic feet per second. The dam's condition assessment is currently unavailable, but it undergoes inspections every 5 years to ensure its integrity. With a moderate risk assessment score of 3, Lewis Dam remains an essential water resource for the surrounding area, offering recreational opportunities and contributing to the local ecosystem. Its location in a picturesque setting makes it a popular destination for water resource and climate enthusiasts to explore and appreciate.

Dam Length

490

Dam Height

28

River Or Stream

TRIB FARMERS FORK

Primary Dam Type

Earth

Surface Area

10

Drainage Area

0.27

Nid Storage

133.5

Outlet Gates

None

Hazard Potential

Low

Foundations

Soil

Nid Height

28
       
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.