Marion Prison Lake Dam Reservoir Report

Last Updated: December 5, 2025

Marion Prison Lake Dam, located in Marion, Illinois, is a vital water resource structure designed by Hanson Engineers.


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Summary

Completed in 1991, this Federal-owned Earth dam serves the primary purpose of water supply, with a storage capacity of 601 acre-feet and a surface area of 37 acres. The dam stands at a height of 26 feet and spans 695 feet in length, regulating the flow of the TRIB LIMB BRANCH stream.

Managed by the Illinois Department of Natural Resources, Marion Prison Lake Dam is subject to regular state inspections, permitting, and enforcement to ensure its structural integrity and safety. With a significant hazard potential and moderate risk assessment, emergency action plans have been prepared to address potential threats. Despite facing some regulatory challenges, the dam continues to play a crucial role in water management for the Williamson County region.

Water resource and climate enthusiasts are drawn to Marion Prison Lake Dam for its strategic location and impact on the local ecosystem. As a key water supply infrastructure in the area, the dam's operational efficiency and maintenance are crucial factors in sustaining water resources and mitigating environmental risks. With a robust design and state-regulated oversight, Marion Prison Lake Dam stands as a testament to effective water management practices in Illinois.

Year Completed

1991

Dam Length

695

Dam Height

26

River Or Stream

TRIB LIMB BRANCH

Primary Dam Type

Earth

Surface Area

37

Drainage Area

0.4

Nid Storage

601

Outlet Gates

None

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

26
       
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.