Florida’s Lake Okeechobee has been crowned the dirtiest lake in the US, with cloudy, lead-tainted waters, while Lake Superior takes the title as the cleanest, clearest, and most pristine.
A new study from vacation rental platform Lake.com analyzed water quality data from the National Water Quality Monitoring Council (NWQMC) for the 100 largest lakes in America, collected between January 2020 and July 2025. Researchers looked at eight common indicators of cleanliness — including dissolved oxygen, lead, phosphorus, turbidity (cloudiness), and pH — to find out which lakes are safest and most pleasant to swim in. Only 46 lakes had enough recent data to be ranked.
Lake Okeechobee: murky waters and lead contamination
Lake Okeechobee’s water tested with a turbidity of 34.36 NTU — the second-cloudiest reading of all lakes studied — and contained 0.67 µg/L of lead, which has no safe exposure level. The lake also showed elevated phosphorus levels (0.18 mg/L), which can encourage algae blooms that further reduce water clarity.
The rest of the dirtiest list
Second place went to American Falls Reservoir in Idaho, which appears clear but contains ammonia (0.15 mg/L), a chemical that’s harmful to fish at higher concentrations.
Lake Texoma, straddling Texas and Oklahoma, ranked third due to low oxygen levels (4.42 mg/L), high sulfate content (164.05 mg/L), and heavy total dissolved solids (753.59 mg/L) that give the water a mineral-heavy taste and odor.
Other lakes in the top 10 dirtiest include Oklahoma’s Eufaula Lake, Alaska’s Lake Clark, Florida’s Lake George, Utah Lake, Oneida Lake in New York, Pyramid Lake in Nevada (with record-setting dissolved solids of 5,488 mg/L), and Richland-Chambers Reservoir in Texas.
Lake Superior: America’s clean-water champion
At the other end of the spectrum, Lake Superior topped the cleanest list. It boasts crystal-clear water with near-perfect clarity (0.46 NTU turbidity), low mineral content (44.04 mg/L TDS), and high oxygen levels (10.45 mg/L). Phosphorus was almost undetectable.
Runners-up for cleanest lake include Washington’s Lake Chelan, Georgia–South Carolina’s Lake Hartwell, Missouri’s Lake of the Ozarks, Idaho’s Lake Pend Oreille, and Minnesota’s Lake Winnibigoshish.
Overall state of America’s lakes
On average, large US lakes had healthy oxygen levels (7.29 mg/L) and moderate turbidity (9.54 NTU), though total dissolved solids averaged 504.05 mg/L. About half the tested lakes contained ammonia, and roughly one in four had measurable lead.
David Ciccarelli, CEO of Lake.com, said large lakes appear to have lower mineral and sulfate content than smaller ones but higher ammonia levels compared to last year’s findings. “Generally speaking, large lakes remain very clean and safe to swim in,” Ciccarelli said, “though it’s always wise to check local advisories before diving in.”
Top 3 dirtiest lakes in America
- Lake Okeechobee (FL)
- American Falls Reservoir (ID)
- Lake Texoma (OK/TX)
Top 3 cleanest lakes in America
- Lake Superior (MI/MN/WI/ON)
- Lake Chelan (WA)
- Lake Hartwell (GA/SC)
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