Lake Mendota At Madison Reservoir Report

Last Updated: December 6, 2025

Lake Mendota is a glacial lake located in Madison, Wisconsin with a surface area of 9,842 acres.


°F

°F

mph

Wind

%

Humidity

Summary

The lake is over 450ft deep and is a popular location for fishing, ice skating, and water sports. The lake's hydrology is heavily influenced by precipitation, snowpack, and surface run-off from the surrounding land, which is primarily agricultural. The Yahara River is the primary surface flow provider and is responsible for over 90% of the water entering the lake. The lake has a rich history, with Native American tribes inhabiting the area for thousands of years before European settlement. In the early 20th century, the lake was heavily polluted, but efforts to reduce agricultural runoff and sewage have improved its water quality. Lake Mendota remains an important resource for fishing, recreation, and research in Wisconsin.

Reservoir Details

Gage Height, Ft 24hr Change -0.68%
Percent of Normal 97%
Minimum 7.32 ft
2024-01-14
Maximum 12.36 ft
2008-06-16
Average 9 ft
Dam_Height 16
Hydraulic_Height 5
Drainage_Area 254
Years_Modified 1959 - Other
Year_Completed 1849
Nid_Storage 160000
Structural_Height 16
River_Or_Stream YAHARA RIVER
Surface_Area 9730
Hazard_Potential High
Dam_Length 100
Primary_Dam_Type Other
Length_Of_Locks 102
Nid_Height 16
       
Seasonal Comparison
Gage Height, Ft Levels

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.