Mountain Lake Reservoir Report
Nearby: Eagle Lake Bennett Wma
Last Updated: December 13, 2025
Mountain Lake, located in Cottonwood, Minnesota, is a state-regulated dam with a significant hazard potential and a satisfactory condition assessment.
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Summary
Built in 1960 by the MNDNR, this buttress-type dam stands at a height of 15 feet and has a storage capacity of 1832 acre-feet. The dam serves purposes beyond flood control, with a normal storage capacity of 1145 acre-feet and a surface area of 230 acres.
Situated on the Blue Earth River-TR, Mountain Lake plays a crucial role in managing water resources in the area, with a drainage area of 9.9 square miles and a maximum discharge of 400 cubic feet per second. Despite its uncontrolled spillway type and significant hazard potential, the dam has not undergone modifications in recent years and is inspected every four years to ensure its operational integrity.
Managed by the Minnesota state regulatory agency MNDNR EWR, Mountain Lake's risk assessment is moderate, indicating a need for ongoing risk management measures. With its location in a scenic landscape and vital role in water resource management, this dam serves as a focal point for water resource and climate enthusiasts interested in sustainable infrastructure development and risk mitigation strategies.
Year Completed |
1960 |
Dam Length |
25 |
Dam Height |
10 |
River Or Stream |
BLUE EARTH RIVER-TR |
Primary Dam Type |
Other |
Surface Area |
230 |
Hydraulic Height |
5 |
Drainage Area |
9.9 |
Nid Storage |
1832 |
Structural Height |
15 |
Hazard Potential |
Significant |
Foundations |
Unlisted/Unknown |
Nid Height |
15 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Des Moines River At Jackson
|
55cfs |
Cottonwood River Near New Ulm
|
215cfs |
Minnesota River At New Ulm
|
1130cfs |
Little Cottonwood River Near Courtland
|
33cfs |
Watonwan River Near Garden City
|
82cfs |
Minnesota River At Morton
|
1750cfs |
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.
Mountain Lake