Is your lake healthy?
Water quality report cards for 4,564 lakes across Minnesota and Wisconsin. Every lake graded A through F based on clarity, phosphorus, and algae levels.
Cleanest Lakes
Lakes Needing Attention
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Grade Distribution
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?
All 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.
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 (how deep you can see). Phosphorus fuels algae growth — higher levels mean more algae risk. Chlorophyll-a directly measures algae concentration in the water.
Why does my lake have a "limited data" badge?
Lakes with only one of the three metrics available receive a grade based on that single metric, with a "limited data" indicator. Lakes with 2-3 metrics get a full composite grade.