A popular vehicle decal says the Great Lakes are “unsalted and shark-free.”
Is it true?
Not if you consider road salt and salt from water softeners. In 2021, scientific researchers estimated chlorides in Lake Michigan had risen from about 1-2 milligrams per liter before European settlement to more than fifteen milligrams per liter. Canadian researchers found levels ranging from 1.4 milligrams in Lake Superior to 133 milligrams per liter in Lake Ontario. Although these levels are well below the chloride concentrations in ocean water (about thirty-five grams per liter) and below the aesthetic standard for chlorides in drinking water (about 250 milligrams per liter) rising concentrations of chlorides may have ecological effects. These include killing or damaging aquatic plants and invertebrates.
The study of Lake Michigan salinity levels found that watersheds with a greater area of roads, parking lots and other impervious surfaces tended to have higher chloride levels due to direct runoff into streams and lakes.
Although road salt is likely the largest single source of chloride pollution of the Great Lakes, livestock, fertilizer, and water softeners also contribute. Still, the easiest solution to rising chloride levels in the Great Lakes is to use less road salt, and transportation officials have searched for ways to apply less salt on roads during the winter, while keeping roads clear and safe for motorists. The most direct way is to put salt on fewer roads. In some cases, sand or ash is used as an alternative to rock salt in lower-traffic areas.
As for sharks, well, there was a report of a bite taken out of a Chicago-area man by a bull shark on Jan. 1, 1955. The best guess of the Chicago Tribune is that it was a hoax published in 1975, the year the movie Jaws was released. So “shark-free” is accurate.
