Data Report · Updated August 2026
Of 33,763 monitored lakes across 36 US states, 5,873 carry nutrient and algae readings. 50.4% of those sampled lakes sit in EPA's favourable condition classes; 31.5% in its poorer ones. 27,890 carry no nutrient reading: insufficient evidence, not a poor one. Minnesota holds the largest catalog (6,760 lakes). Michigan has the highest share of lakes in EPA's favourable condition classes among states with enough sampled water to rank.
Every figure on this page is computed from the same lake records the rest of LakeQuality publishes. The universe is the 36 US states whose agencies report enough lake sampling to publish readings for — 33,763 named lakes with a public page. It is not every lake in the United States. Most US waterbodies have never been sampled for these nutrients.
13 more state hubs — Maryland, Maine, South Carolina, California, Connecticut, New Hampshire, New Jersey, Rhode Island, Delaware, West Virginia, Louisiana, Mississippi, and Alaska — already have named-lake pages. They are not in this table, because their records have not yet cleared the same sampling minimum used everywhere else here. The Canadian provinces have their own pages, with provincial measurements. They are not US states. Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador.
Two denominators appear throughout. Rated is the set with enough sampling to publish a reading (5,873 lakes, 17.4% of the edition). All monitored is every named lake in those 36 states, including lakes with no reading. A percentage of “good water” is always of the sampled set. Treating a missing reading as a poor one would invent 27,890 poor readings the samples do not support.
Phosphorus, nitrogen, chlorophyll-a and turbidity are read against EPA National Lakes Assessment 2022 ecoregion condition classes. Secchi depth is measured and shown because that is what a swimmer sees; EPA assigns it no condition class. Of the 33,763 named lakes in this edition, 5,873 carry a nutrient or algae reading and 27,890 do not. A share of “good water” is always of the sampled set: treating an unmeasured lake as a poor one would say more than the samples support.
EPA's favourable condition classes for nutrients and algae cover 50.4% of the sampled lakes, and its poorer classes 31.5%. The middle of that range is the everyday American lake: fair water, visible green in a warm July, generally usable and not the postcard clarity of a northern oligotrophic basin. None of it is a swimming clearance, and none of it is a judgement on a shoreline. Both ends still need a same-day look at algae advisories and the lake's own page. Full method: methodology and where the data comes from.
Carlson's Trophic State Index classifies a lake by how much algae its nutrient load can support. We state a class as fact only on sampled lakes, which is the same sampling requirement as the readings. Clarity-only TSI estimates exist on thousands of unsampled waters; publishing those as “eutrophic” would say more than the samples support. Of the 5,830 classified lakes in this edition:
| Class | What it usually looks like | Lakes | Share |
|---|---|---|---|
| oligotrophic | Low nutrients, deep clarity, the classic northern blue lake | 716 | 12.3% |
| mesotrophic | Moderate nutrients, a green tint in late summer, a typical Midwestern lake | 1,971 | 33.8% |
| eutrophic | High nutrients, regular algae, the default farm-belt and southern reservoir | 2,366 | 40.6% |
| hypereutrophic | Very high algae, frequent scums, short Secchi readings | 777 | 13.3% |
Eutrophic and hypereutrophic lakes together are 53.9% of the classified set. Oligotrophic lakes are 12.3%. That is the country's real split: most monitored US lakes are productive waters, not wilderness gin-clear basins. The oligotrophic share concentrates in deep glacial belts — Michigan, Minnesota's forested north, Vermont, and high-elevation western lakes. The eutrophic share is the agricultural Midwest and the naturally warm South. See trophic state explained.
Census Bureau regions, counting only the states we cover in each. The Midwest holds 51.7% of the lakes in this edition. The South has the highest share in EPA's favourable classes among sampled lakes (53.4%). A region average is a landscape average. Deep glacial water and shallow prairie reservoirs are not the same object, and an average does not pretend they are.
The glacial lake belt from Minnesota through the Great Lakes states, plus the prairie pothole and farm-belt reservoirs.
12 states. Minnesota contributes 6,760 lakes. Michigan leads the region on the favourable-class share (84.6%). Trends: 1,652 improving, 1,616 declining.
The Southeast, Gulf Coast, and south-central plains — naturally productive waters, including Florida’s subtropical lakes.
10 states. Florida contributes 3,122 lakes. Florida leads the region on the favourable-class share (69.4%). Trends: 854 improving, 989 declining.
The Rockies, Great Basin, and Pacific Northwest — high-elevation glacial and snowmelt lakes plus desert reservoirs.
10 states. Montana contributes 865 lakes. Wyoming leads the region on the favourable-class share (78.1%). Trends: 180 improving, 211 declining.
New England and the Mid-Atlantic — glacial lakes, Adirondack waters, and older reservoirs.
4 states. New York contributes 1,613 lakes. Vermont leads the region on the favourable-class share (68.5%). Trends: 98 improving, 47 declining.
Florida is the South's weight (3,122 lakes, 69.4% in EPA's favourable classes of 1,302 sampled). Those favourable readings sit toward the lower end of the favourable band rather than the top, which is what the subtropical thresholds are for: Florida LAKEWATCH breakpoints, not Minnesota thresholds. A naturally productive warm-water lake should not flunk because it is not a glacial kettle. The same state is also heavily 303(d)-listed (28.1%) — the listing and the readings are answering different questions, which is the national pattern in miniature.
Ranked by the share of sampled lakes in EPA's favourable condition classes. A state average is treated as a ranking only when at least 20 lakes carry a reading (6 states fall below that bar and stay in the table with a note). Open any row for the named lakes behind the average.
| # | State | Region | Lakes | Rated | Avg | % favourable | % poorer | % 303(d) | ↑ / ↓ | Cleanest named lake |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Michigan | midwest | 3,392 | 182 | 84.6% | 5.5% | 11.3% | 204/165 | Crystal Lake | |
| 2 | Wyoming | west | 731 | 64 | 78.1% | 15.6% | 0.5% | 38/32 | Boysen Reservoir Transitional Embayment | |
| 3 | Florida | south | 3,122 | 1,302 | 69.4% | 23.4% | 28.1% | 596/705 | Jacc Lake | |
| 4 | Wisconsin | midwest | 3,133 | 824 | 69.2% | 15.3% | 12.4% | 499/349 | Green Lake | |
| 5 | Vermont | northeast | 308 | 111 | 68.5% | 4.5% | 24% | 76/31 | Lake St. Catherine | |
| 6 | New York | northeast | 1,613 | 22 | 63.6% | 13.6% | 24.7% | 16/6 | Queneska Island Lake | |
| 7 | Massachusetts | northeast | 829 | 81 | 50.6% | 30.9% | 46.9% | 5/10 | — | |
| 8 | Montana | west | 865 | 36 | 50% | 25% | 3.9% | 9/48 | Tally Lake | |
| 9 | Minnesota | midwest | 6,760 | 1,501 | 48.8% | 30.7% | 23.9% | 713/828 | Rainy Lake | |
| 10 | Nebraska | midwest | 592 | 51 | 43.1% | 49% | 14.9% | 17/21 | Lake C W Mcconaughy | |
| 11 | Utah | west | 304 | 96 | 40.6% | 31.3% | 19.1% | 32/47 | Flaming Gorge Reservoir | |
| 12 | Alabama | south | 422 | 74 | 39.2% | 31.1% | 10.4% | 14/39 | Smiw Lake | |
| 13 | Virginia | south | 390 | 126 | 38.9% | 24.6% | 30.3% | 77/45 | Mouth of Witcher Cr. Lake | |
| 14 | South DakotaThin sample | midwest | 469 | 3 | 33.3% | 33.3% | 11.5% | 0/1 | Traverse Lake | |
| 15 | Missouri | midwest | 451 | 165 | 30.9% | 49.7% | 29.3% | 68/70 | Sherwood Lake | |
| 16 | Kentucky | south | 189 | 79 | 30.4% | 27.8% | 34.9% | 9/49 | Lake Beshear | |
| 17 | ArizonaThin sample | west | 229 | 7 | 28.6% | 28.6% | 13.1% | 13/13 | Ak-Chin Reservoir | |
| 18 | Colorado | west | 733 | 54 | 24.1% | 44.4% | 10.4% | 11/8 | Pueblo Reservoir | |
| 19 | WashingtonThin sample | west | 792 | 18 | 22.2% | 55.6% | 19.3% | 16/12 | Banks Lake | |
| 20 | Oregon | west | 659 | 55 | 21.8% | 63.6% | 19% | 25/20 | Odell Lake | |
| 21 | North Dakota | midwest | 826 | 87 | 20.7% | 36.8% | 5.9% | 19/30 | Wheaton Lake | |
| 22 | IdahoThin sample | west | 301 | 15 | 20% | 53.3% | 13.3% | 9/4 | Black Cnyn Reservoir Ns of | |
| 23 | Pennsylvania | northeast | 570 | 63 | 19% | 49.2% | 14.9% | 1/0 | Belmont Lake | |
| 24 | Indiana | midwest | 387 | 74 | 18.9% | 40.5% | 21.4% | 4/8 | Lake George | |
| 25 | Georgia | south | 693 | 32 | 18.8% | 9.4% | 3.3% | 1/24 | Lake Worth | |
| 26 | NevadaThin sample | west | 223 | 16 | 18.8% | 50% | 13% | 11/14 | Illipah Reservoir | |
| 27 | Illinois | midwest | 594 | 96 | 18.8% | 75% | 40.7% | 10/7 | Lake Calumet | |
| 28 | Kansas | midwest | 239 | 87 | 18.4% | 67.8% | 54.4% | 33/56 | Hillsdale Lake | |
| 29 | New MexicoThin sample | west | 326 | 17 | 17.6% | 35.3% | 12.3% | 16/13 | Mescalero Lake Deep | |
| 30 | Texas | south | 1,376 | 84 | 14.3% | 65.5% | 2.8% | 26/41 | Lake Hawkins | |
| 31 | Iowa | midwest | 330 | 156 | 12.8% | 76.9% | 37% | 82/78 | West Okoboji Lake | |
| 32 | North Carolina | south | 395 | 148 | 12.2% | 58.1% | 7.3% | 19/19 | Lake Waccamaw | |
| 33 | Ohio | midwest | 292 | 31 | 9.7% | 67.7% | 1.4% | 3/3 | Caesar Creek Lake | |
| 34 | Arkansas | south | 632 | 64 | 9.4% | 62.5% | 6% | 38/31 | Beaver Lake | |
| 35 | Tennessee | south | 277 | 28 | 3.6% | 67.9% | 10.5% | 14/7 | Piney River Lake | |
| 36 | Oklahoma | south | 319 | 24 | 0% | 91.7% | 0% | 60/29 | Lake Texoma |
Among states with enough rated water to rank, Michigan leads on the favourable-class share (84.6% of 182 sampled lakes). That is mostly landscape: Michigan sits on deep glacial water and forested catchments. Reading any state's number as a scorecard on a single agency is the wrong use of the table.
Minnesota is the catalog, not the trophy: 6,760 named lakes (20% of the edition), 48.8% in the favourable condition classes and 30.7% in the poorer ones. A state that samples thousands of waters will always look more mixed than a state that reports a few dozen mountain reservoirs. Density is a feature of the monitoring program, and it is why a national average without the state table is easy to misread.
Kansas has the highest 303(d) share among rankable states (54.4%). That listing rate and the favourable-class rate can both be high in the same state — Florida is the working example — because mercury and nutrients are different lists. The thin-sample rows (South Dakota, Arizona, Washington, Idaho, Nevada, New Mexico) are in the table so the coverage map is honest, not so a two-lake average can headline a ranking.
National named-lake lists, US only, clean ranking names, complete readings. The state table is the typical lake. These lists are the exceptions. Each name links to the measurements.
Cleanest combined nutrient and algae readings, 2026. Live ranking: cleanest lakes.
Highest chlorophyll-a. A hotspot is a measurement, not a same-day bloom advisory.
Deepest Secchi reading. Clarity is shown, not scored. Live ranking: clearest lakes.
A trend is published only where a lake has enough repeated summer samples to call a direction on clarity, phosphorus, or chlorophyll-a. Of 7,206 lakes with a call, 2,784 are improving, 2,863 are declining, and 1,559 are stable. The two moving sides are nearly the same size. That is the honest national sentence: US lake water is not collapsing in this dataset, and it is not being rescued all at once either.
Among rankable states, 14 have more improving lakes than declining ones (Michigan, Wyoming, Wisconsin, Vermont, New York, Virginia, …). 14 have the opposite tilt (Florida, Massachusetts, Montana, Minnesota, Nebraska, Utah, …). Improvements usually mean fewer nutrients reaching the water — upgraded wastewater, shoreline buffers, phosphorus kept on the field. Declines run the other way: new shoreline, heavier farm runoff, warmer summers that lengthen the algae season. The named movers: comeback lakes and lakes that are slipping.
6,089 lakes in this edition (18%) appear on an EPA/state 303(d) impaired-waters list (3,521 formally listed, 3,259 with a TMDL or cleanup plan). That rate is higher than the poorer-class rate because the two systems measure different things. The readings are nutrients and algae. The list is whatever designated use the state assessed — including toxics the nutrient readings never see.
The most common listed cause is Mercury (2,758 lakes). Nutrients follow (2,236). Algal growth is listed on 930 lakes. Mercury in fish tissue is why a clean northern lake can still carry a consumption advisory. Pathogens are why a clear lake can still close a beach. Read the nutrient and algae readings for nutrients and algae; read the 303(d) row and the fish-advisory explainer for everything those readings are blind to. Per-state lists start at /impaired/mn.
If you are choosing a place to swim, start with the lakes in EPA's favourable classes in the state you can actually reach, then check a current advisory. The readings tell you where the water usually sits. It does not tell you whether a calm, hot week produced a scum this morning. The swimming guide is here; the seasonal algae picture is here.
If you are fishing, a long species list and clean readings can travel together or apart. Mercury and PFAS are tissue contaminants. A clean-looking lake can still be a catch-and-release water for the species you wanted to keep. Start from the lake page and the state advisory, not from the national average.
If you are looking at shoreline property, the useful move is the lake's own multi-year record, the readings, trend and 303(d) causes, and how often algae is measured — not the state average. Neighboring lakes in the same county routinely read far apart on nutrients. The property checklist is here.
This edition covers monitored lakes in 36 US states — 33,763 named waters, 5,873 of them with an EPA condition class. It is not a census of every US lake. 13 more states have named-lake pages on the site but are not in this table yet, because their sampling record does not clear the same minimum. The Canadian provinces have their own pages, with provincial measurements. They are not US states.
50.4% of the 5,873 sampled lakes sit in EPA's favourable condition classes for nutrients and algae in their ecoregion. 31.5% sit in EPA's poorer classes. Shares are of rated lakes only. The 27,890 lakes with no nutrient reading (82.6%) are EPA Integrated Reporting Category 3, not a poor reading.
Among states with at least 20 rated lakes, Michigan has the highest share in EPA's favourable classes (84.6% of 182 rated lakes). State averages reflect geology and land use as much as any one management program. Open Michigan’s full report for the named lakes behind the average.
Of the 7,206 monitored lakes with a multi-year trend, 2,784 are improving, 2,863 are declining, and 1,559 are holding steady. Water quality moves over years, not weeks. A national split this close means the typical lake is not racing toward either pole.
18% of the lakes in this edition appear on an EPA/state 303(d) impaired-waters list. The most common listed cause is Mercury (2,758 lakes). The EPA condition class covers nutrients and algae, not mercury, PFAS, or bacteria. A lake with clean nutrient readings can still be listed for a contaminant those readings do not measure.
No. Measured phosphorus, nitrogen, chlorophyll-a and turbidity are read against EPA National Lakes Assessment ecoregion classes. It is blind to mercury, PFAS, E. coli, and same-day bloom advisories. Check the lake page, the state advisory, and any posted beach notice before you swim or keep a fish.
Each sampled lake is read against its EPA condition class on measured nutrients and algae, total phosphorus, nitrogen, chlorophyll-a, and turbidity — drawn from the EPA Water Quality Portal and state environmental agencies, then classified against EPA National Lakes Assessment 2022 ecoregion condition classes. Northern-tier states use that national scale; Florida uses Florida LAKEWATCH breakpoints for naturally productive subtropical lakes. Secchi clarity is shown and is not scored. Lakes without enough evidence are UNRATED, not given an F. Full method: methodology. The narrative companion to this data edition is The State of America’s Lakes 2026.
Cite this report: LakeQuality, “The State of America’s Lakes 2026,” lakequality.org/report. Data: EPA Water Quality Portal + state agencies. Edition covers 33,763 monitored lakes in 36 US states.
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Coverage note: this report covers monitored lakes in 36 enabled US states, not every lake in the United States, and not the 13 dark-catalog hubs. The readings reflect the most recent multi-year sampling available and update as new agency data is ingested. An EPA condition class is a classification of measured data, never a swim or consumption clearance.