Thompson Lake Dam Reservoir Report

Last Updated: December 5, 2025

Thompson Lake Dam, also known as Millsite Dam, is a privately owned earth and gravity dam located in Livingston County, Michigan.


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Summary

Built in 1894, this dam serves primarily for recreational purposes, providing a tranquil and scenic environment for water resource and climate enthusiasts to enjoy. Situated in Howell, Michigan, the dam stands at a height of 19.5 feet and has a storage capacity of 2,320 acre-feet, with a surface area of 260 acres and a drainage area of 10.1 square miles.

Managed by the Michigan Department of Environment, Great Lakes, and Energy (DEGLE), Thompson Lake Dam is regulated, permitted, inspected, and enforced by the state to ensure its safety and functionality. With a controlled spillway and a maximum discharge capacity of 222 cubic feet per second, the dam presents a significant hazard potential, categorized as "Very High (1)" in terms of risk assessment. Despite its fair condition assessment as of November 2018, Thompson Lake Dam continues to be a popular destination for outdoor recreation, attracting visitors interested in water resources and climate-related activities in the area.

Year Completed

1894

Dam Length

200

Dam Height

19.5

River Or Stream

Tributary to Bogue Creek

Primary Dam Type

Earth

Surface Area

260

Hydraulic Height

18.5

Drainage Area

10.1

Nid Storage

2320

Structural Height

19.5

Hazard Potential

Significant

Nid Height

20
       
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.