St Ansgar Milldam Reservoir Report
Nearby: Otranto Dam Mitchell Mill Dam
Last Updated: December 13, 2025
St Ansgar Milldam, located in Mitchell, Iowa, along the Cedar River, is a historic gravity dam completed in 1919 primarily for recreation purposes.
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Summary
The dam stands at a height of 9 feet and spans 202 feet, with a storage capacity of 600 acre-feet and a drainage area of 780 acres. Despite being categorized as having a low hazard potential, the dam is subject to state regulation and inspection by the Iowa DNR to ensure its safety and integrity.
While the dam does not have a spillway, it is equipped with uncontrolled spillway type to manage water flow during high water events. The risk assessment for St Ansgar Milldam is moderate, indicating a level 3 risk, with no specific risk management measures or emergency action plan currently in place. The dam's condition assessment is listed as "Not Rated", highlighting the need for further evaluation and potential improvements to enhance its safety and resilience in the face of changing climate conditions and increasing water resource challenges.
Overall, St Ansgar Milldam serves as both a recreational and structural asset in the community, offering opportunities for outdoor activities and water-based recreation. As climate change continues to impact water resources and infrastructure, ongoing monitoring and maintenance of the dam will be crucial to ensure its continued function and safety for the surrounding area. Enthusiasts of water resources and climate adaptation will find St Ansgar Milldam to be an intriguing case study in the intersection of historical preservation, recreational use, and the evolving challenges of climate resilience in dam management.
Year Completed |
1919 |
Dam Length |
202 |
Dam Height |
9 |
River Or Stream |
CEDAR RIVER |
Primary Dam Type |
Gravity |
Surface Area |
55 |
Drainage Area |
780 |
Nid Storage |
600 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
9 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Cedar River Near Austin
|
117cfs |
Winnebago River At Mason City
|
166cfs |
Cedar River At Charles City
|
450cfs |
Little Cedar River Near Ionia
|
70cfs |
Shell Rock River At Shell Rock
|
484cfs |
Cedar River At Waverly
|
436cfs |
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.
Halvorson County Park Campground
Otranto County Park Campground
Interstate County Park Campground
Riverside County Park Campground
Osage Sprink Park Campground
St Ansgar Milldam