Lake Lancelot Dam Reservoir Report

Last Updated: December 5, 2025

Lake Lancelot Dam, located in Mapleton-Offstream, Illinois, is a private dam with a primary purpose of recreation.


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Summary

Built in 1971 by ASSOCIATED ENGINEERS, INC., this earth dam stands at a height of 54 feet and has a length of 750 feet. With a storage capacity of 1271 acre-feet, the dam is situated on the TRIB WEST BRANCH LAMARSH CREEK, offering a surface area of 48 acres for water enthusiasts to enjoy.

Managed by the Illinois Department of Natural Resources, Lake Lancelot Dam has a spillway width of 23 feet and a maximum discharge capacity of 2315 cubic feet per second. The dam's hazard potential is classified as high, with a moderate risk assessment rating. Although the condition assessment is currently not available, the dam is regularly inspected by state authorities, with the last inspection conducted in May 2021.

For water resource and climate enthusiasts looking to explore a recreational water source in Peoria County, Illinois, Lake Lancelot Dam offers an opportunity to appreciate the beauty of nature while understanding the importance of dam safety and management. With its picturesque surroundings and significant storage capacity, this dam serves as a vital asset for both local residents and visitors seeking a peaceful retreat by the water.

Year Completed

1971

Dam Length

750

Dam Height

54

River Or Stream

TRIB WEST BRANCH LAMARSH CREEK

Primary Dam Type

Earth

Surface Area

48

Drainage Area

2.8

Nid Storage

1271

Outlet Gates

Uncontrolled

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

54
       
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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.