The Chicago Park District has taken a precaution against bacteria.
Officials have issued a swim ban at all Chicago area beaches following an overnight flash flood encouraged them to open locks in Wilmette and Downtown Chicago.
"When locks are opened, the flow of the Chicago River is reversed and storm water mixed with sewage may be released into Lake Michigan,' a statement said. "Once the locks close, the Chicago Park District will begin water sampling, twice daily and every day, until test results show low levels of bacteria in the water."
Check the Chicago Park District web site for up to date information on when the beaches reopen.