Mazomanie Reservoir Report

Last Updated: December 5, 2025

Mazomanie, also known as Lake Marion Outlet, is a local government-owned dam located in Dane County, Wisconsin.


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Summary

Built in 1851, this earthen dam sits on the Black Earth Creek and serves primarily for recreational purposes, offering a surface area of 20 acres and a normal storage capacity of 50 acre-feet. With a dam height of 14 feet and a hydraulic height of 8 feet, Mazomanie has a drainage area of 35.2 square miles and a maximum discharge of 50 cubic feet per second.

Despite its long history, Mazomanie poses a high hazard potential and has been rated as unsatisfactory in terms of its condition assessment. The dam underwent modifications in 1971, and its last inspection was conducted in January 2013. With a very high risk assessment rating, it is crucial for the structure to undergo regular inspections and maintenance to ensure its safety and the protection of downstream areas. The dam is regulated by the Wisconsin Department of Natural Resources and is subject to state permitting, inspection, and enforcement.

Water resource and climate enthusiasts in Mazomanie can appreciate the historical significance and recreational value of this dam while also recognizing the importance of its maintenance and risk management. As a key element in the local water infrastructure, Mazomanie serves as a reminder of the ongoing challenges and responsibilities in managing water resources effectively in the face of changing climate conditions. By staying informed and engaged in the monitoring and maintenance of structures like Mazomanie, enthusiasts can contribute to the sustainable management of water resources for future generations.

Years Modified

1971 - Other

Year Completed

1851

Dam Length

1200

Dam Height

14

River Or Stream

BLACK EARTH CREEK

Primary Dam Type

Earth

Surface Area

20

Hydraulic Height

8

Drainage Area

35.2

Nid Storage

100

Structural Height

14

Hazard Potential

High

Nid Height

14
       
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.