Lake Mattoon Dam Reservoir Report
Last Updated: December 21, 2025
Lake Mattoon Dam, located in Effingham, Illinois, is a significant earth dam completed in 1957 with a primary purpose of recreation and water supply.
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Summary
Managed by the local government, the dam stands at a height of 46 feet and spans a length of 2250 feet, providing a storage capacity of 22,569 acre-feet and serving a drainage area of 57 square miles. The dam's spillway, with a width of 350 feet, is uncontrolled, allowing for a maximum discharge of 28,273 cubic feet per second into the Little Wabash River.
With a hazard potential classified as significant and a moderate risk assessment level, Lake Mattoon Dam is subject to state regulation, inspection, and enforcement by the Illinois Department of Natural Resources. The dam's condition assessment is currently unavailable, and an Emergency Action Plan was last revised in 2004. Despite its age, the dam continues to play a crucial role in water resource management and recreational activities in the region, drawing the attention of water resource and climate enthusiasts for its design by Wilson & Anderson Engineers and its impact on the local ecosystem.
Year Completed |
1957 |
Dam Length |
2250 |
Dam Height |
46 |
River Or Stream |
LITTLE WABASH RIVER |
Primary Dam Type |
Earth |
Surface Area |
980 |
Drainage Area |
57 |
Nid Storage |
22569 |
Outlet Gates |
Uncontrolled |
Hazard Potential |
Significant |
Foundations |
Unlisted/Unknown |
Nid Height |
46 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Lake Mattoon Dam