Jefferson Reservoir Report

Last Updated: December 5, 2025

Jefferson is a gravity dam located in Jefferson, Wisconsin, along the Rock River.


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Summary

Completed in 1842, this dam serves primarily for recreation purposes, providing a surface area of 122 acres and a maximum storage capacity of 650 acre-feet. With a hydraulic height of 6 feet and a structural height of 11 feet, Jefferson has a controlled spillway with a width of 182 feet. The dam has a low hazard potential and was last inspected in October 2013, with a satisfactory condition assessment reported in January 2014.

Managed by the local government, Jefferson is regulated by the Wisconsin Department of Natural Resources, with state permitting, inspection, and enforcement in place. The dam has undergone modifications in 1915 and 2001. Despite being categorized as having a very high risk level, measures for risk management and emergency preparedness are not explicitly mentioned in the data. The dam is within the jurisdiction of Rep. F. James Sensenbrenner Jr. (R) and falls under the supervision of the Rock Island District of the US Army Corps of Engineers.

Enthusiasts of water resources and climate in the Jefferson area can appreciate the historical significance and recreational opportunities provided by the Jefferson dam. With its long-standing presence and vital role in water management along the Rock River, ensuring the continued safety and effectiveness of Jefferson remains a priority for local authorities and regulatory agencies. The data highlights the importance of regular inspections, maintenance, and risk assessment to mitigate potential hazards and protect the surrounding community and environment.

Years Modified

1915 - Other, 2001 - Other

Year Completed

1842

Dam Length

250

Dam Height

11

River Or Stream

ROCK

Primary Dam Type

Gravity

Surface Area

122

Hydraulic Height

6

Drainage Area

1074

Nid Storage

650

Structural Height

11

Hazard Potential

Low

Nid Height

11
       
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.