Updated Aug 2026 · 37,603 lakes
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Cabins and rentals near lakes with the lowest nutrient and algae readings. Pick a town or lake, or search as-is.
New · Annual data report
The State of America’s Lakes 2026
5,737 lakes with nutrient and algae readings — the clearest water, the lowest algae, and the biggest improvers among the lakes with multi-year nutrient and algae readings.
Cleanest lake
Sunset Lake
Rutland County, VT
Lakes with nutrient and algae readings
5,737
of 37,603 tracked. Readings are the agency’s own, shown as reported.
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Measured lakes by US state
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Alberta, Saskatchewan, Manitoba, New Brunswick, Prince Edward Island, Yukon, Northwest Territories and Nunavut are not listed. No licensed lake-chemistry record for those places is published here.
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Each country hub publishes the rating its own national or EU authority issued, attributed to that agency.
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Frequently asked questions
How are the water-quality readings classified?
Each lake's nutrient and algae readings — total phosphorus, total nitrogen, chlorophyll-a, and turbidity — are shown beside the EPA National Lakes Assessment 2022 condition class for that lake's own ecoregion, so a reading is compared against the lakes it would naturally resemble. LakeQuality publishes no letter grade. Water clarity (Secchi depth) is measured and shown in feet on every lake page but is not scored: EPA assigns no condition class to Secchi depth, and dark water can come from algae, from natural dissolved colour, or from suspended clay. A lake without recent nutrient or algae sampling shows whatever measurements exist rather than an estimate. The full cutpoint table, the condition-class thresholds and the sampling behind each reading are on our methodology page.
Where does the water-quality data come from?
Clarity (Secchi depth), total phosphorus and chlorophyll-a readings come from the EPA Water Quality Portal and the state agencies that sample each lake, and are shown as those agencies report them. 5,737 of 37,603 tracked lakes have nutrient or algae readings; 1,524 more carry a water-clarity estimate from satellite imagery. Where a government body has published its own class for a lake, that class is shown. LakeQuality does not issue swimming clearances; state and county advisories are the authority for that.
Where does the data come from?
Water quality data for US lakes comes from the EPA Water Quality Portal, which aggregates monitoring results from state environmental agencies across all 49 covered states (including the Minnesota Pollution Control Agency and Wisconsin DNR), the USGS, and other federal programs. Canadian lakes come from the Ontario Ministry of the Environment, Conservation and Parks and Québec's RSVL programme instead. Lake depth comes from the Minnesota DNR LakeFinder and Wisconsin DNR; fish species data covers Minnesota, Wisconsin, and Michigan.
How often is the data updated?
Data is sourced from the EPA Water Quality Portal covering the most recent years of monitoring. Readings reflect the median of summer-season (June–September) measurements.
What does each measurement mean?
Total phosphorus and total nitrogen are the nutrients that feed algae growth. Chlorophyll-a measures the algae itself, so it is the response the EPA condition class leans on hardest. Turbidity measures how much suspended material is in the water. Secchi depth measures water clarity in feet — how far down you can see — and is reported alongside the cause limiting it, rather than scored.
Is it safe to swim in a lake with high nutrient readings?
No reading on this site is a swimming clearance. Clarity, phosphorus and chlorophyll-a describe nutrients and algae; they do not measure E. coli, cyanotoxins, or a posted beach closure. Whether a lake is safe to swim in today is a call for the state water agency and the county health department, so check current local advisories before you get in, especially in late summer when blooms peak.
What is trophic state?
Trophic state describes how productive a lake is. The published class comes from median chlorophyll-a against EPA's national bands: oligotrophic at or below 2 µg/L (very low productivity, clear water), mesotrophic above 2 and up to 7, eutrophic above 7 and up to 30 (high productivity, frequent algae), and hypereutrophic above 30 (dense algae). The classic Carlson Trophic State Index is still calculated and shown for continuity, and both sit beside the nutrient and algae readings.
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