Updated May 2026
Is your lake healthy?
LakeQuality grades every monitored lake across 12 states — water clarity in feet, lake depth, fish species, swimming safety, and A-F report cards based on EPA and state agency data.
Water quality report cards for 5,243 lakes across 12 states.
Fish Species
3,028 lakes with documented fish species. Find the best lakes for your target species.
State Parks
Every Minnesota and Wisconsin state park linked to nearby graded lakes — find a place to camp, hike, and fish.
Water Quality Rankings
Explore lakes by water quality, depth, clarity, and more.
Top 500 U.S. Lakes by Water Quality (2026)
The 500 highest-scoring lakes across 12 states in one spreadsheet — overall grade, water clarity, phosphorus, chlorophyll-a, and trophic state index, ranked from cleanest, drawn from the EPA Water Quality Portal and state DNR surveys. Enter your email for the CSV.
Latest DNR Fisheries Reports
Newest scientific surveys and resources from Minnesota and Wisconsin DNR. 5,243 reports indexed across 128 counties — browse all →
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
Minnesota
2,209 lakes graded across 74 counties
Wisconsin
1,405 lakes graded across 69 counties
Illinois
144 lakes graded across 45 counties
Michigan
628 lakes graded across 61 counties
Iowa
169 lakes graded across 75 counties
Ohio
17 lakes graded across 9 counties
Pennsylvania
3 lakes graded across 3 counties
New York
176 lakes graded across 47 counties
Missouri
316 lakes graded across 78 counties
Indiana
22 lakes graded across 7 counties
North Dakota
150 lakes graded across 48 counties
South Dakota
4 lakes graded across 3 counties
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.
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