Lewis Reservoir Report

Last Updated: December 6, 2025

Lewis is a privately owned dam located in Polk, Wisconsin, along the Knapp Creek.


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Summary

Built in 1931, this Earth dam serves primarily for recreational purposes, with a normal storage capacity of 130 acre-feet and a maximum discharge of 757 cubic feet per second. The dam stands at a height of 16 feet and spans 50 feet in length, providing a surface area of 35 acres for activities such as fishing and boating.

Managed by the Wisconsin Department of Natural Resources (WIDNR), Lewis Dam has a low hazard potential and is considered to be in fair condition as of the last assessment in May 2020. Despite its age, the dam has undergone modifications in 1955 to ensure its structural integrity. With ongoing state regulation, inspection, and enforcement in place, Lewis Dam continues to be a safe and enjoyable recreation spot for visitors.

While the dam poses a low risk in terms of potential hazards, its location within a very high-risk area (Risk Assessment Level 1) highlights the importance of consistent monitoring and maintenance. The dam's controlled spillway, along with its fair condition assessment and regular inspection schedule, contribute to the overall safety of the structure. As an essential part of the local water resource infrastructure, Lewis Dam remains a vital asset for the community and a popular destination for water resource and climate enthusiasts.

Years Modified

1955 - Other

Year Completed

1931

Dam Length

50

Dam Height

16

River Or Stream

Knapp Creek

Primary Dam Type

Earth

Surface Area

35

Hydraulic Height

11

Drainage Area

7

Nid Storage

300

Structural Height

16

Hazard Potential

Low

Nid Height

16
       
Seasonal Comparison

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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.