Cottonwood Lake Reservoir Report
Nearby: Lost Marsh Wma Perch Lake
Last Updated: December 6, 2025
Cottonwood Lake, located in Blue Earth, Minnesota, is a state-regulated dam with a low hazard potential and a satisfactory condition assessment.
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Summary
Built in 1938 by Ducks Unlimited and part of an old WPA dam, this gravity dam stands at 7 feet tall and stretches 625 feet in length. With a normal storage capacity of 533 acre-feet and a drainage area of 1.7 square miles, Cottonwood Lake serves as a vital water resource in the area.
The dam's primary purpose is listed as "Other," and it is designed with a controlled spillway with a width of 10 feet. The maximum discharge capacity of the dam reaches 359 cubic feet per second, ensuring effective flood control measures for the surrounding area. Despite its age, Cottonwood Lake remains a critical infrastructure for managing water resources and climate-related risks in the region.
With a very high risk assessment rating of 1, Cottonwood Lake is closely monitored with regular inspections every 8 years to ensure its structural integrity and functionality. Although the dam poses a low hazard potential, the risk management measures in place help mitigate any potential threats. As an essential component of the local water infrastructure, Cottonwood Lake plays a significant role in safeguarding the community against floods and other water-related emergencies.
Year Completed |
1938 |
Dam Length |
625 |
Dam Height |
6 |
River Or Stream |
BIG COBB RIVER-TR |
Primary Dam Type |
Gravity |
Surface Area |
213 |
Hydraulic Height |
3.4 |
Drainage Area |
1.7 |
Nid Storage |
1172 |
Structural Height |
7 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
7 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Le Sueur River Near Rapidan
|
179cfs |
Blue Earth River Near Rapidan
|
328cfs |
Minnesota River At Mankato
|
2870cfs |
Watonwan River Near Garden City
|
82cfs |
Little Cottonwood River Near Courtland
|
33cfs |
Cottonwood River Near New Ulm
|
215cfs |
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.
Cottonwood Lake