Marissa Reservoir Dam Reservoir Report

Last Updated: December 21, 2025

Marissa Reservoir Dam, located in New Athens, Illinois, is a significant earth dam completed in 1938 for the primary purpose of recreation.


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Summary

Managed by the local government, this dam stands at a height of 22 feet and spans a length of 400 feet, providing a storage capacity of 134 acre-feet. The dam is regulated by the Illinois Department of Natural Resources and undergoes regular inspections to ensure its safety and compliance with state standards.

With a spillway type classified as 'Uncontrolled' and an outlet gate system also operating as 'Uncontrolled', the dam poses a significant hazard potential. Despite this, the risk assessment for Marissa Reservoir Dam is categorized as moderate, with a risk management plan in place to address any potential issues. The dam's location on the TRIB MUD CREEK tributary and its proximity to St. Clair County make it a vital water resource for the region, supporting both recreational activities and water supply needs. Enthusiasts of water resources and climate will find Marissa Reservoir Dam a fascinating structure to study and monitor for its environmental impact and management practices.

Year Completed

1938

Dam Length

400

Dam Height

22

River Or Stream

TRIB MUD CREEK

Primary Dam Type

Earth

Nid Storage

134

Outlet Gates

Uncontrolled

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

22
       
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.