America’s Cleanest and Dirtiest Lakes: 2026 Report on Lake Pollution and Water Quality
Lake has released our 2026 report ranking the cleanest and dirtiest lakes in the United States. Discover why Lake Chelan ranks #1 on the cleanest lakes list, and get acquainted with the factors that influence a lake’s position on the cleanest list and the dirtiest list.
Driving the News
- Lake Chelan is the cleanest lake in America, due to its low mineral levels and low turbidity.
- The Great Salt Lake is the dirtiest lake in the US right now, with by far the heaviest mineral load of any ranked lake (134,500 mg/L Total Dissolved Solids), as well as the lowest dissolved oxygen levels (3.65 mg/L) and the highest ammonia levels of any lake in the top ten dirtiest (0.92 mg/L).
- Over 60 major lakes in America were assessed across eight different categories.
The Cleanest and Dirtiest Lakes at a Glance
A new report has revealed the cleanest and dirtiest lakes in America, with Lake Chelan ranking as the cleanest, while the Great Salt Lake in Utah ranks as the dirtiest due to its saline levels.
The study, conducted by vacation rental platform Lake.com, analyzed all the available chemical data from the National Water Quality Monitoring Council (NWQMC) for 100 of America’s largest lakes, sampled from January 1st, 2021, until July 30th, 2026. The study evaluated eight of the most commonly measured characteristics that can indicate a lake’s cleanliness level:
- Dissolved oxygen
- Ammonia
- Lead
- Phosphorus
- Sulfate
- Total dissolved solids
- Turbidity
- pH levels
A total of 67 lakes reported at least three of these pollution factors and therefore qualified for the study. The findings were put into an index to produce a pollution score out of 10 to determine the safest and most dangerous lakes based on hygiene, pollution and more.
Key Highlights
- Lake Chelan is the cleanest lake in America.
- The Great Salt Lake is the dirtiest lake in the US right now.
- Over 60 major lakes in America were assessed across eight different categories.
Top 10 Cleanest Lakes in the USA Ranked
U.S. water quality • pollution score /10
Lake Chelan is the only lake in the data to score a perfect 0 — the next cleanest, Lake Superior, still registers 0.28
Composite pollution score across the 10 cleanest U.S. lakes, built from dissolved oxygen, ammonia, lead, phosphorus, sulfate, total dissolved solids, turbidity, and pH deviation. Lower is cleaner.
Washington
Michigan–Minnesota–Wisconsin–Ontario
Alabama
Minnesota–Ontario
Washington
British Columbia–Montana
Illinois–Indiana–Michigan–Wisconsin
Georgia–South Carolina
Michigan–Ontario
Kentucky–Tennessee
At the other end of the scale, Lake Chelan in Washington state is the cleanest lake in America. Lake Chelan has turbidity of just 2.00 NTU, meaning it’s extremely clear, and one of the lowest TDS levels at 30.25 mg/L. Lake Chelan also experiences low sulfate levels of 3.65 mg/L.
However, Lake Superior, which was the cleanest lake in last year’s report, ranks a close second with the lowest turbidity of any lake (0.54 NTU), low TDS levels (74 mg/L), and high oxygen levels (10.58 mg/L).
Top 10 Dirtiest Lakes in the USA Ranked
U.S. water quality • pollution score /10
Great Salt Lake tops the list with the highest pollution score, 10 out of 10 — 43% higher than the next dirtiest lake
Composite pollution score across the 10 most degraded U.S. lakes, built from dissolved oxygen, ammonia, lead, phosphorus, sulfate, total dissolved solids, turbidity, and pH deviation.
Utah
Nebraska
Wisconsin
Minnesota
North Dakota
North Carolina
Missouri
Utah
California
Arkansas–Missouri
The Great Salt Lake in Utah is America’s dirtiest lake. Its water carries an extremely high mineral load, with total dissolved solids (TDS) of 134,500 mg/L, which is much more than any other lake in the study. TDS refers to the total minerals within water, including sulfates, chlorides, calcium, magnesium, potassium, bicarbonates and sodium, and indicates the general quality of water. While not necessarily a direct indicator of pollution itself, the levels highlight how dangerous it could be to ingest any water from the Great Salt Lake due to its extreme chemistry.
The Great Salt Lake is also the most poorly oxygenated lake in the ranking, with dissolved oxygen of just 3.65 mg/L. If this level were to drop below 2, the lake would become hypoxic, meaning fish would suffocate. It also reports the highest ammonia of any lake in the top ten dirtiest ranking at 0.92 mg/L, along with elevated lead at 2.09 µg/L. The Great Salt Lake is not a freshwater lake and is a terminal lake; therefore, there is no outlet for any mineral or chemical buildup.
Lake McConaughy in Nebraska and Lake Winnebago in Wisconsin rank second and third dirtiest, respectively. Lake McConaughy has turbidity levels of 5.50 NTU, while Lake Winnebago, Wisconsin’s largest inland lake, is ranked so low due to its high levels of phosphorus, which are 0.09 mg/L, along with a pH deviation of 1.58.
The fourth dirtiest lake in America is Lake Vermilion in Minnesota. Lake Vermilion is the second least oxygenated lake, behind the Great Salt Lake, with dissolved oxygen of just 3.90 mg/L.
Devils Lake in North Dakota is the fifth dirtiest lake in the country and is likely to be the smelliest of all, as it has the highest levels of sulfate (639 mg/L) due to no natural outlet to dilute sulfates over time. The smell of sulfate is often described as similar to ‘rotten egg’.
Despite ranking as the eighteenth dirtiest lake overall, Lake Moultrie in South Carolina is the most lead-contaminated lake included in the study, with samples detecting lead at 17.2 µg/L. There is no safe level of lead.
Lake Mattamuskeet in North Carolina shows the highest ammonia of any freshwater lake in the top ten, estimated at 0.67 mg/L. Ammonia should not be present at all in clean water, and when levels reach 0.53 mg/L, the water begins to become harmful to fish.
“America’s largest lakes remain, on the whole, clean and pleasant to swim in. Even the lakes at the top of our dirtiest table sit within the range you would expect for large natural bodies of water, which shows that there is good maintenance and care for them.
“However, with that in mind, some monitoring of lakes throughout the country is uneven from one lake to the next, so anyone looking to visit a lake, particularly swimmers, needs to check any signage near their local swimming spot and follow the advice given to them. No lake in the ranking is inherently dangerous, but you could be at risk of a stomach bug.”
David Ciccarelli, CEO of Lake.com
Notes for Editors
Sources: Lake.com via the National Water Quality Monitoring Council.
Credit with link: If you use this story, please ensure to include a linked mention of Lake.com.
Publisher: The report was compiled by Lake.com, the vacation rental platform offering 75,000 properties near the water across North America and Europe, where families experience the great outdoors.
Methodology
This study uses data from waterqualitydata.us to rank the 100 largest US lakes by surface area based on how dirty they are.
Each lake was ranked using a score calculated with the following equally-weighted factors:
- Dissolved Oxygen Concentration;
- Ammonia Concentration;
- Lead Concentration;
- Phosphorus Concentration;
- Sulfate Concentration;
- Total Dissolved Solids;
- Turbidity;
- Difference from pH of 7.
The study used the most recent 12-month median for each indicator, drawn from data reported between January 1st, 2021 and July 30th, 2026.
Lakes with fewer than three factors available in the official data were excluded, resulting in a ranked list of 67 of the largest lakes in the US whose cleanliness could be measured.
The lakes were ranked based on a total pollution score, whereby the higher the pollution score, the dirtier the lake was considered.
Map for the Cleanest Lakes in America
Source Data for the Cleanest Lakes in America
U.S. water quality • cleanest lakes ranked
The 10 cleanest U.S. lakes by composite pollution score, led by Lake Chelan at 0.00
Eight water-quality indicators roll up into the composite score in the final column. A dash marks an indicator not reported for that lake.
| # | Lake | State | Dissolved oxygen (mg/L) |
Ammonia (mg/L) |
Lead (µg/L) |
Phosphorus (mg/L) |
Sulfate (mg/L) |
Total dissolved solids (mg/L) |
Turbidity (NTU) |
Diff. from pH 7 |
Pollution score /10 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Lake Chelan | Washington | 9.45 | – | – | – | 3.65 | 30.25 | 2.00 | 0.02 | 0.00 |
| 2 | Lake Superior | Michigan–Minnesota–Wisconsin–Ontario | 10.58 | 0.07 | 0.29 | 0.01 | 12.20 | 74.00 | 0.54 | 0.78 | 0.28 |
| 3 | Lake Martin | Alabama | 8.15 | 0.04 | – | 0.01 | – | 29.00 | 1.28 | 0.13 | 0.53 |
| 4 | Rainy Lake | Minnesota–Ontario | 8.85 | – | – | – | 1.95 | 45.00 | – | 0.12 | 0.62 |
| 5 | Franklin D. Roosevelt Lake | Washington | 9.95 | 0.03 | 0.18 | 0.02 | 9.72 | 89.83 | 1.36 | 1.14 | 0.72 |
| 6 | Lake Koocanusa | British Columbia–Montana | 9.85 | 0.02 | 0.23 | 0.00 | 25.90 | 152.75 | 1.60 | 1.25 | 0.84 |
| 7 | Lake Michigan | Illinois–Indiana–Michigan–Wisconsin | 10.60 | 0.08 | 0.61 | 0.01 | 24.00 | 183.00 | 1.17 | 1.30 | 0.87 |
| 8 | Lake Hartwell | Georgia–South Carolina | 8.30 | 0.06 | – | 0.03 | – | – | 1.54 | 0.15 | 1.01 |
| 9 | Lake Huron | Michigan–Ontario | 9.73 | 0.01 | 0.08 | – | 18.00 | 199.00 | 3.45 | 1.23 | 1.07 |
| 10 | Kentucky Lake | Kentucky–Tennessee | – | 0.04 | – | – | 6.75 | 76.50 | 5.25 | 1.11 | 1.08 |
Map for the Dirtiest Lakes in America
Source Data for the Dirtiest Lakes in America
U.S. water quality • dirtiest lakes ranked
Great Salt Lake tops the list at a pollution score of 10.00, driven by sulfate and total dissolved solids levels far above the rest of the group
Eight water-quality indicators roll up into the composite score in the final column. A dash marks an indicator not reported for that lake.
| # | Lake | State | Dissolved oxygen (mg/L) |
Ammonia (mg/L) |
Lead (µg/L) |
Phosphorus (mg/L) |
Sulfate (mg/L) |
Total dissolved solids (mg/L) |
Turbidity (NTU) |
Diff. from pH 7 |
Pollution score /10 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Great Salt Lake | Utah | 3.65 | 0.92 | 2.09 | 0.42 | 285.00 | 134,500.00 | – | 1.05 | 10.00 |
| 2 | Lake McConaughy | Nebraska | 5.59 | – | – | – | – | – | 5.50 | 1.45 | 6.97 |
| 3 | Lake Winnebago | Wisconsin | 8.46 | – | – | 0.09 | – | – | – | 1.58 | 6.21 |
| 4 | Lake Vermilion | Minnesota | 3.90 | – | – | – | 11.20 | – | – | 0.66 | 5.75 |
| 5 | Devils Lake | North Dakota | 9.22 | 0.10 | 5.00 | – | 639.00 | 1,490.00 | – | 1.67 | 5.51 |
| 6 | Lake Mattamuskeet | North Carolina | – | 0.67 | – | 0.08 | – | – | 23.50 | – | 5.16 |
| 7 | Truman Reservoir | Missouri | 7.92 | – | – | 0.04 | – | – | – | 1.26 | 5.11 |
| 8 | Utah Lake | Utah | 8.36 | 0.08 | 0.09 | – | 231.50 | 1,060.00 | 65.55 | 1.56 | 4.82 |
| 9 | Clear Lake | California | 7.08 | 0.48 | – | 0.33 | 9.69 | 180.40 | 13.70 | 1.20 | 4.80 |
| 10 | Table Rock Lake | Arkansas–Missouri | 8.76 | – | – | 0.01 | – | – | – | 1.37 | 4.52 |
Contact Details
Should you require any further information, please do not hesitate to contact Maddie Peacey at [email protected].
For more information about Lake.com, please contact Sarah Stahl at [email protected].
