Lake Chelan in Washington has been named the cleanest large lake in the US, while Utah’s Great Salt Lake ranked as the dirtiest, according to a new analysis by vacation rental platform Lake.com.
The study analysed chemical data from the National Water Quality Monitoring Council for 100 of America’s largest lakes between 1st January 2021 and 30th July 2026. Researchers evaluated eight cleanliness indicators: dissolved oxygen, ammonia, lead, phosphorus, sulfate, total dissolved solids, turbidity, and pH levels. 67 lakes provided data on at least three factors to qualify for the ranking, receiving a pollution score out of 10, with lower scores indicating cleaner water.
Nation’s Cleanest Lakes
Lake Chelan claimed the top spot with a perfect score of 0, showing a turbidity of 2.00 NTU, a total dissolved solids reading of 30.25 mg/L, and sulfate levels of 3.65 mg/L. Lake Superior ranked second with a score of 0.28, recording the lowest turbidity of any lake at 0.54 NTU, total dissolved solids of 74 mg/L, and dissolved oxygen of 10.58 mg/L.
The top 10 cleanest lakes
| Rank | Lake | State(s) | Pollution Score /10 |
| 1 | Lake Chelan | Washington | 0.00 |
| 2 | Lake Superior | Michigan, Minnesota, Wisconsin, Ontario | 0.28 |
| 3 | Lake Martin | Alabama | 0.53 |
| 4 | Rainy Lake | Minnesota, Ontario | 0.62 |
| 5 | Franklin D. Roosevelt Lake | Washington | 0.72 |
| 6 | Lake Koocanusa | British Columbia, Montana | 0.84 |
| 7 | Lake Michigan | Illinois, Indiana, Michigan, Wisconsin | 0.87 |
| 8 | Lake Hartwell | Georgia, South Carolina | 1.01 |
| 9 | Lake Huron | Michigan, Ontario | 1.07 |
| 10 | Kentucky Lake | Kentucky, Tennessee | 1.08 |
Highest pollution scores
The Great Salt Lake received the maximum pollution score of 10. As a terminal saline lake with no outlet, minerals and chemicals accumulate over time through evaporation. Total dissolved solids reached 134,500 mg/L, dissolved oxygen stood at a study-low 3.65 mg/L, lead reached 2.09 µg/L, and ammonia measured 0.92 mg/L, the highest among the top 10 dirtiest lakes. The study noted that while its high mineral load is largely natural, its extreme chemistry makes ingesting the water potentially dangerous.
The top 10 dirtiest lakes
| Rank | Lake | State | Pollution Score /10 |
| 1 | Great Salt Lake | Utah | 10.00 |
| 2 | Lake McConaughy | Nebraska | 6.97 |
| 3 | Lake Winnebago | Wisconsin | 6.21 |
| 4 | Lake Vermilion | Minnesota | 5.75 |
| 5 | Devils Lake | North Dakota | 5.51 |
| 6 | Lake Mattamuskeet | North Carolina | 5.16 |
| 7 | Truman Reservoir | Missouri | 5.11 |
| 8 | Utah Lake | Utah | 4.82 |
| 9 | Clear Lake | California | 4.80 |
| 10 | Table Rock Lake | Arkansas, Missouri | 4.52 |
Notable chemical findings
Among other surveyed bodies of water, Lake McConaughy recorded a turbidity of 5.50 NTU. Lake Winnebago showed phosphorus levels of 0.09 mg/L and a pH deviation of 1.58. Lake Vermilion registered dissolved oxygen of 3.90 mg/L, the second lowest behind the Great Salt Lake. Lacking a natural outlet, Devils Lake recorded the highest sulfate levels at 639 mg/L, a factor often associated with a rotten egg smell.
Lake Mattamuskeet recorded the highest ammonia level among freshwater lakes in the top 10 at 0.67 mg. Ammonia should be absent from clean water and becomes harmful to fish at 0.53 mg/L. Although ranking 18th overall for dirtiness, Lake Moultrie in South Carolina recorded the study’s highest lead concentration at 17.2 µg/L, a chemical with no safe threshold.
David Ciccarelli, chief executive of Lake.com, emphasised that most major bodies of water remain safe: “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.”
“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 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.”
The report was compiled by Lake.com, which offers 75,000 properties near water across North America and Europe.