The Natural Resources Defense Council found the second-worst-rated beach in the country is in the north suburbs.
At Elder Lane Park Beach in Winnetka, 54 percent of water samples fail to meet the state's maximum bacterial standards.
Tests at North Point Marina Beach in Lake County failed 34 percent of the time.
Beaches in the city of Chicago rated better. Rainbow, Montrose and South Shore beaches all had failure rates between 24 and 22 percent.