Delton Reservoir Report

Last Updated: December 5, 2025

Delton, also known as Mirror Lake, is a gravity dam located in Lake Delton, Wisconsin, with a primary purpose of recreation.


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Summary

Completed in 1931, this structure boasts a height of 19 feet and a hydraulic height of 14 feet, with a storage capacity of 1280 acre-feet. The dam spans 150 feet in length and is situated on Dell Creek, serving as a controlled spillway with a width of 127 feet.

Despite its age, Delton remains in fair condition with a low hazard potential, as indicated by a recent assessment in October 2020. The dam has a very high risk assessment rating of 1, highlighting the importance of ongoing monitoring and maintenance. While it is not under the jurisdiction of the US Army Corps of Engineers, the Wisconsin Department of Natural Resources regulates, inspects, and enforces compliance with state permitting requirements to ensure the safety and integrity of the structure for both recreational and environmental purposes. Overall, Delton stands as a significant water resource in the area, contributing to the local landscape and providing opportunities for outdoor activities.

Year Completed

1931

Dam Length

150

Dam Height

19

River Or Stream

DELL CREEK

Primary Dam Type

Gravity

Surface Area

137

Hydraulic Height

14

Drainage Area

71

Nid Storage

1280

Structural Height

19

Hazard Potential

Low

Nid Height

19
       
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.