Willow River Reservoir Report
Nearby: Thunder Lake Loon Lake
Last Updated: December 5, 2025
Located in Cass, Minnesota, Willow River, also known as Big Rice Lake, is a state-owned dam with a primary purpose of irrigation.
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Summary
Built in 1962, this gravity dam stands at 8 feet high and spans 45 feet in length. With a normal storage capacity of 5,409 acre-feet and a maximum storage of 13,465 acre-feet, the dam serves a critical role in regulating the flow of the Willow River.
Managed by the Minnesota Department of Natural Resources, Willow River is subject to state regulation, inspection, and enforcement to ensure its structural integrity and operational efficiency. Despite being classified as having a low hazard potential, the dam has a very high risk assessment rating, emphasizing the importance of ongoing risk management measures. The condition assessment in 2018 deemed the dam to be in satisfactory condition, highlighting the diligent efforts to maintain its safety and functionality for the surrounding community.
With a drainage area of 96 square miles and a maximum discharge capacity of 1,700 cubic feet per second, Willow River plays a vital role in water resource management in the region. The controlled spillway design and the presence of emergency action plans further demonstrate the commitment to safeguarding the dam and the downstream areas in the event of a potential emergency. For water resource and climate enthusiasts, Willow River serves as a fascinating example of the intersection of infrastructure, environmental stewardship, and risk management in the face of changing climatic conditions.
Year Completed |
1962 |
Dam Length |
45 |
Dam Height |
8 |
River Or Stream |
WILLOW RIVER |
Primary Dam Type |
Gravity |
Drainage Area |
96 |
Nid Storage |
13465 |
Structural Height |
9 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
9 |
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 |
Mississippi River Near Bemidji
|
169cfs |
Crow Wing River At Nimrod
|
279cfs |
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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