Furnace Bridge Reservoir Report

Last Updated: December 5, 2025

Furnace Bridge, also known as Lower Mayville, is a gravity-type dam located in Mayville, Wisconsin, along the East Branch Rock River.


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Summary

Built in 1848, this dam serves primarily for recreational purposes, with a height of 14 feet and a length of 180 feet. The dam has a significant hazard potential, with a fair condition assessment as of May 2020.

Managed by the Wisconsin Department of Natural Resources, Furnace Bridge is state-regulated, permitted, inspected, and enforced to ensure safety and compliance. With a maximum storage capacity of 140 acre-feet and a normal storage of 68 acre-feet, the dam plays a crucial role in water resource management for the surrounding area. The dam's spillway is controlled, with a width of 93 feet, and it has a very high risk classification according to the data provided.

Overall, Furnace Bridge is a historic structure that not only provides recreational opportunities but also plays a vital role in water storage and management in Dodge County, Wisconsin. With its significant hazard potential and very high risk classification, it is essential for authorities to continue monitoring and maintaining this dam to ensure the safety of the surrounding community and the sustainability of the water resources it impacts.

Years Modified

1905 - Other

Year Completed

1848

Dam Length

180

Dam Height

14

River Or Stream

EAST BRANCH ROCK

Primary Dam Type

Gravity

Surface Area

17

Hydraulic Height

10

Drainage Area

172

Nid Storage

140

Structural Height

14

Hazard Potential

Significant

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.