This great Lake Superior wave shot comes courtesy of Shannon Kivi of 906 Images, who in August 2025 caught a sparkling series of waves along the Upper Peninsula shore driven by a north wind.
A report done by a vacation rental platform, Lake.com, has declared Lake Superior the cleanest large lake in the United States.
“Lake Superior is the nation’s cleanest, thanks to its oxygen-rich (10.45 mg/L), clear (34.36 NTU turbidity) and low-minerals water (44.04 mg/L Total Dissolved Solids),” the organization noted in announcing its Cleanest & Dirtiest Lakes, adding, “Lake Superior Registers Virtually Zero Pollution.”
The study conducted Lake.com analyzed chemical data from the National Water Quality Monitoring Council for 100 of America’s largest lakes, sampled from Jan. 1, 2020, to July 15, 2025, and evaluated eight characteristics "that can suggest a lake’s cleanliness level: dissolved oxygen, ammonia, lead, phosphorus, sulfate, total dissolved solids (TDS), turbidity and pH.”
Catherine O’Reilly, director of the Large Lakes Observatory at the University of Minnesota Duluth, helped us to unpack the conclusion of Lake.com, plus gave additional insights into monitoring lakes big and small. The study data, she said, comes from a big EPA-managed national lakes assessment done every five years and sampling a wide range of factors, including chemicals that are not considered in the Lake.com report.
“The Lake.com report does use important metrics of water quality that are traditionally considered good indicators. To support healthy lake environments, you generally want pretty clear water (so low turbidity and total dissolved solids) that has high dissolved oxygen levels. Low nutrient concentrations (nitrogen, phosphorus) means that you are less likely to have large amounts of algae. The things they are considering here are found naturally in all lakes, with the exception of high levels of lead.
“In general, if you have good water quality in a lake, you probably also have low levels of other manmade pollutants as well,” she said, but added, “There are things that we generally consider pollutants, such as microplastics and PFAS (the ‘forever’ chemicals), that are found in Lake Superior.”
Catherine gave as an example the story “PFAS are raining down on Lake Superior” by Pam Wright for Quetico Superior Wilderness News that talks about spreading pollutants via rain.
“The concentration of these pollutants, along with things like the herbicide atrazine, is low relative in Lake Superior compared to other lakes. So, in that sense, yes, Lake Superior is an incredibly clean lake. We are very lucky and hope we are able to keep it that way!”
Being big can also help lakes battle pollution, Catherine says. “Large lakes tend to be cleaner than smaller lakes (hence the old adage "dilution is the solution to pollution"), but once they are polluted, it takes much more work to get them clean, because there is so much water that has to flush out of the lake. Also, many metals and manmade pollutants stick to the sediments, making it pretty much impossible to recover and treat when the lake is large. If you have a clean lake, the most economically effective thing to do is to keep it clean, making sure that very few pollutants enter into it."