Plymouth Reservoir Report

Last Updated: December 5, 2025

Plymouth, located in Sheboygan, Wisconsin, is home to a gravity dam on the Mullet River that was completed in 1951 for recreational purposes.


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Summary

The dam stands at a height of 14 feet with a hydraulic height of 9 feet and a structural height of 14 feet, creating a reservoir with a storage capacity of 110 acre-feet and a normal storage of 70 acre-feet. With a surface area of 36 acres and a drainage area of 58.6 square miles, the dam has a maximum discharge capacity of 550 cubic feet per second and a spillway type classified as controlled.

Despite its age, the Plymouth dam has a low hazard potential and was assessed to be in fair condition as of May 2020. The risk assessment for the dam is very high, with a ranking of 1, indicating the importance of ongoing monitoring and maintenance. The last inspection took place in October 2013, with regular inspections scheduled every 10 years. With its picturesque location and recreational purpose, the Plymouth dam serves as a vital asset for both the local community and visitors, highlighting the intersection of water resource management and climate resilience in the region.

Year Completed

1951

Dam Length

150

Dam Height

14

River Or Stream

MULLET

Primary Dam Type

Gravity

Surface Area

36

Hydraulic Height

9

Drainage Area

58.6

Nid Storage

110

Structural Height

14

Hazard Potential

Low

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.