Chicago beaches have less bacteria thanks to invasive mollusk, study says
Levels of E. coli have dropped at near every beach along Lake Michigan, including those in Chicago, according to a recently released study. An invasive mollusk may be responsible. The Michigan State University study looked at water quality from 45 Lake Michigan beaches from 2000 to 2014. It found that levels of E. coli dropped an average of 10.8 percent, leading to fewer closures.
Almost all of Chicago’s beaches on Lake Michigan had a decrease, with Montrose Beach being an exception. All 27 Chicago beaches are slated to open Friday for the season, conditions pending.
While there are a variety of factors that may have contributed to the improvement, the researchers point to the rise of the quagga mussel — which found its way over to the Great Lakes from the Black Sea region — as the likeliest reason for improvement.
“They are carpeting the bottom of the lake,” said co- author Chelsea Weiskerger. The mussel filters the water of bacteria, making it clearer, which in turn allows more sunlight to penetrate. The sunlight also helps fight bacteria.
Chicago Park District officials weren’t aware of the results of the study but did note that it also saw improvements in E. coli levels, crediting its own efforts to control birds, who are the primary source of E. coli, and promoting efforts to fight waste and litter.
“It’s going to be a beautiful weekend,” said Cathy Breitenbach, the Park District’s director of cultural and natural resources. “We encourage people to do their part.”
Both Breitenbach and Weiskerger acknowledge that beaches are all different and require a different approach to manage bacteria in the water. Montrose Beach, which has had a slight uptick in E. coli which the study says wasn’t significant, is different because of its nature as both a flat and curved beach.
Breitenbach also said the Park District made some design changes at the beach in Humboldt Park, the city’s only inland beach that grappled with high levels of E. coli in 2017 because it was difficult to wash away.
Keep track of beach openings and closings at the Park District website, chicagoparkdistrict. com/ parks- facilities/ beaches/