The 10 Cleanest Lakes in the U.S., Ranked by Water Quality

There are millions of lakes in the continental United States that provide spots for swimming, boating, kayaking, fishing, and more. But one is cleaner than all the rest.

The largest freshwater lake in the world, Lake Superior was named the cleanest in the country thanks to its oxygen rich, clear water and low mineral content, according to a study by Fishbox, a fishing forecast platform, that was shared with Travel + Leisure. Lake Superior, which flows into Michigan, Minnesota, and Wisconsin, is also renowned for its fishing: ice fishing in the winter and summer catches that include bass, salmon, trout, and walleye.

“We are pleased to find that, generally speaking, large lakes remain very clean and safe to swim and fish in, though monitoring any signage near swimming spots and adhering to the indicated advice may save you from catching a rare but nasty stomach bug,” Fishbox’s CEO Serge Selezen said in a statement shared with T+L. “Clean water isn’t just about human recreation, it’s about maintaining the delicate balance that keeps our fish populations thriving.” 

In second place was Lake Chelan in Washington, which the study found had “optimal” pH levels for both swimming and freshwater aquatic life. That was followed by Lake Hartell, which straddles Georgia and South Carolina, Lake of the Ozarks in Missouri, and Lake Pend Oreille in Idaho rounding out the top five.

On the flipside, the study found America’s dirtiest lake was Florida’s Lake Okeechobee. There, an “unnatural” level of lead was detected and its water appeared murky, which the study said may be attributed to high levels of phosphorus, which can stimulate algae growth. 

To come up with its study, Fishbox examined 100 large lakes in the U.S. on a number of factors, including the concentration of dissolved oxygen, ammonia, lead, sulfate, phosphorus, and more. The study drew its data from researchers at the National Water Quality Monitoring Council who sampled chemical data for each lake from between Jan. 1, 2020, and July 15, 2025.

Overall, nearly half of the 100 lakes were found to have at least three pollution factors.

This is the full list of the top 10 cleanest lakes in America, according to Fishbox.

1. Lake Superior; Michigan, Minnesota, Wisconsin
2. Lake Chelan; Washington
3. Lake Hartwell; Georgia, South Carolina
4. Lake of the Ozarks; Missouri
5. Lake Pend Oreille; Idaho
6. Lake Winnibigoshish; Minnesota
7. Kentucky Lake; Kentucky, Tennessee
8. Lake Norman; North Carolina
9. Lake Mead; Arizona, Nevada
10. Flathead Lake; Montana