Nyswonger Dam Reservoir Report

Last Updated: December 8, 2025

Nyswonger Dam, located in Warren County, Iowa, was completed in 1970 and is owned and regulated by a private entity.


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Summary

The dam, designed by the USDA NRCS, serves multiple purposes including fire protection, stock and small fish pond management, and recreation. With a low hazard potential and a moderate risk assessment rating of 3, Nyswonger Dam stands at 30 feet tall and spans 492 feet in length, holding a maximum storage capacity of 74 acre-feet.

Situated on the TR-Middle River, Nyswonger Dam plays a crucial role in water resource management, providing water for various uses while maintaining a surface area of 5.3 acres. Despite its age, the dam has not been rated for its condition and has not undergone recent inspections. However, with state jurisdiction and regulation by the Iowa DNR, Nyswonger Dam remains a key infrastructure for the community of SUMMERSET, offering essential services and recreational opportunities while ensuring the safety and sustainability of the surrounding environment.

As a significant earth dam in the region, Nyswonger Dam operates with an uncontrolled spillway type and a soil foundation. While there are no outlet gates or associated structures, the dam's primary purpose of fire protection and stock management highlights its importance in safeguarding the local area from potential hazards. With a risk management plan in place and a history of moderate risk assessment, Nyswonger Dam continues to demonstrate its value in water resource management and climate resilience efforts within the state of Iowa.

Year Completed

1970

Dam Length

492

Dam Height

30

River Or Stream

TR-MIDDLE RIVER

Primary Dam Type

Earth

Surface Area

5.3

Drainage Area

0.38

Nid Storage

74

Hazard Potential

Low

Foundations

Soil

Nid Height

30
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.