Thunder Lake Reservoir Report
Nearby: Willow River Washburn Lake
Last Updated: December 5, 2025
Nestled in the heart of Cass, Minnesota, Thunder Lake is a captivating water resource that offers a plethora of recreational opportunities for enthusiasts of all ages.
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Summary
This concrete dam, completed in 1934, stands at a height of 18 feet and boasts a normal storage capacity of 7750 acre-feet, providing ample space for water-based activities such as fishing, boating, and swimming. With a surface area of 1347 acres and a drainage area of 16.8 square miles, Thunder Lake is a picturesque destination for those seeking to immerse themselves in the beauty of Minnesota's natural landscape.
Managed by the Minnesota Department of Natural Resources, Thunder Lake is regulated, inspected, and enforced to ensure the safety and sustainability of its water resources. The dam's hazard potential is considered low, with a satisfactory condition assessment as of April 2015. While the dam's primary purpose is recreation, it also serves as a vital component of the local ecosystem, providing habitat for a variety of wildlife and contributing to the overall health of the Willow River-TR watershed. Visitors to Thunder Lake can enjoy its tranquil waters, scenic surroundings, and abundant recreational opportunities while appreciating the importance of responsible water resource management in the face of climate change.
As climate change continues to impact water resources and ecosystems worldwide, Thunder Lake stands as a testament to the importance of sustainable water management practices. With its state-regulated status, satisfactory condition assessment, and low hazard potential, Thunder Lake serves as a model for other recreational water bodies in Minnesota and beyond. Whether you're a climate enthusiast, water resource advocate, or simply a nature lover looking for a serene escape, Thunder Lake offers a unique opportunity to appreciate the beauty and resilience of our natural world in the face of environmental challenges.
Year Completed |
1934 |
Dam Height |
18 |
River Or Stream |
WILLOW RIVER-TR |
Primary Dam Type |
Concrete |
Surface Area |
1347 |
Hydraulic Height |
0.9 |
Drainage Area |
16.8 |
Nid Storage |
8640 |
Structural Height |
5 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
18 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Mississippi River At Grand Rapids
|
633cfs |
Mississippi River At Aitkin
|
1010cfs |
Prairie River Near Taconite
|
63cfs |
Mississippi River At Brainerd
|
972cfs |
Crow Wing River At Nimrod
|
279cfs |
Crow Wing River Near Pillager
|
708cfs |
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.
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