Updated Apr 2026
Is your lake healthy?
LakeQuality grades every monitored lake in Minnesota and Wisconsin, water clarity in feet, lake depth, fish species, swimming safety, and A-F report cards based on state agency data.
Water quality report cards for 3,770 lakes across Minnesota and Wisconsin.
Fish Species
2,754 lakes with documented fish species. Find the best lakes for your target species.
Water Quality Rankings
Explore lakes by water quality, depth, clarity, and more.
Best Lakes For...
Data-driven picks for every activity, filtered by water quality, access, fish, depth, and size.
Cleanest Lakes
Lakes Needing Attention
Browse by State
Grade Distribution
Featured Lakes
Frequently Asked Questions
How are lake grades calculated?
Grades are based on three water quality metrics: water clarity (Secchi depth), phosphorus levels, and chlorophyll-a concentration. Each metric is graded A-F using Metropolitan Council standards established in the 1980s. The overall grade is the average of available metrics.
Where does the data come from?
Water quality data comes from the EPA Water Quality Portal, which aggregates monitoring results from the Minnesota Pollution Control Agency (MPCA), Wisconsin DNR, USGS, and other state and federal agencies. Lake depth, fish species, and physical characteristics come from the Minnesota DNR LakeFinder.
How often is the data updated?
Data is sourced from the EPA Water Quality Portal covering the most recent 5 years of monitoring. Lake grades reflect the median summer season (June-September) measurements.
What does each metric mean?
Secchi depth measures water clarity in feet (how deep you can see). Phosphorus fuels algae growth, higher levels mean more algae risk. Chlorophyll-a directly measures algae concentration in the water.
Is it safe to swim in a lake graded C or below?
Lakes graded C have moderate water quality and are generally safe for swimming, though algae may be present. Lakes graded D or F have poor water quality with high algae risk, swimming is not recommended. Always check local health department advisories.
What is the Trophic State Index?
The Carlson Trophic State Index (TSI) classifies lakes by nutrient levels: oligotrophic (TSI < 40, clear and clean), mesotrophic (40-50, moderate nutrients), eutrophic (50-70, high nutrients and algae), and hypereutrophic (> 70, excessive algae). It is calculated from Secchi depth, phosphorus, and chlorophyll-a.