Loon Lake Reservoir Report

Last Updated: December 5, 2025

Loon Lake, located in Cass County, Minnesota, is a federally owned Earth dam constructed in 1969 by the USDA FS with a primary purpose that falls under the "Other" category.


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Summary

This dam stands at a height of 7 feet and spans 180 feet in length, with a storage capacity of 530 acre-feet. The reservoir's normal storage level is reported to be 370 acre-feet and serves a drainage area of 0.96 square miles, with a low hazard potential and a condition assessment that is currently "Not Rated."

Managed by the St. Paul District of the US Army Corps of Engineers, the dam has not undergone any modifications since its completion and has not been inspected since March 1974. Despite its age, the structure has not been assessed for its current condition, and no emergency action plan or inundation maps have been prepared. The dam poses a low risk due to its condition and hazard potential, but without a recent evaluation, there is uncertainty about its current safety and resilience in the face of potential climate challenges and water resource management issues.

As an integral part of the Willow River watershed, Loon Lake plays a crucial role in water storage and management in the region. Water resource and climate enthusiasts would find Loon Lake an intriguing case study for understanding the complexities of dam infrastructure, federal ownership, and the need for regular inspections and risk assessments to ensure the safety and reliability of critical water resources in Minnesota.

Year Completed

1969

Dam Length

180

Dam Height

7

River Or Stream

WILLOW RIVER-TR

Primary Dam Type

Earth

Drainage Area

0.96

Nid Storage

530

Structural Height

7

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

7
       
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.