Billy Boy Reservoir Report

Last Updated: December 5, 2025

Billy Boy, also known as Bolger, is a gravity dam located in Sawyer, Wisconsin, specifically in the city of Couderay.


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Summary

Completed in 1936, this dam serves primarily for recreation purposes and stands at a height of 13 feet with a hydraulic height of 8 feet. With a storage capacity of 53,600 acre-feet and a normal storage of 28,300 acre-feet, Billy Boy covers a surface area of 8,464 acres and has a drainage area of 110 square miles.

Managed by the local government and regulated by the Wisconsin Department of Natural Resources, Billy Boy has a significant hazard potential with a fair condition assessment as of May 2020. Despite its age, the dam has been inspected regularly, with the last inspection conducted in October 2018. The risk assessment for Billy Boy is categorized as very high, highlighting the importance of ongoing risk management measures to ensure the safety and integrity of the structure.

Situated on the Couderay River, Billy Boy offers a controlled spillway type and a maximum discharge capacity of 910 cubic feet per second. While the dam has not been modified in recent years, its historical significance and role in providing recreational opportunities underscore the importance of continued monitoring and maintenance to safeguard both the environment and surrounding communities.

Year Completed

1936

Dam Length

40

Dam Height

13

River Or Stream

COUDERAY

Primary Dam Type

Gravity

Surface Area

8464

Hydraulic Height

8

Drainage Area

110

Nid Storage

53600

Structural Height

13

Hazard Potential

Significant

Nid Height

13
       
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.