The river will flow temporarily into Lake Michigan, where it'll dump millions of gallons of raw sewage.
Heavy rain in Chicago has maxed out storm water storage facilities and caused officials to "re-reverse" the Chicago River into Lake Michigan, in an effort to lessen flooding in the city.
The river's flow was reversed a century ago to prevent sewage from draining into the city's drinking water source. This, it turns out, is still a very real concern. The Chicago Tribune reports that this reversal will allow "millions of gallons of raw and partially treated sewage to flow into the region's source of drinking water."
Tom LaPorte, a spokesman for the Chicago Department of Water Management, said the city so far has not noticed any unusual contamination in water drawn from intake cribs farther out in the lake.
Department officials are constantly monitoring the situation, LaPorte said, and as a precaution started adding more bacteria-killing chlorine to lake water before pumping it to 7 million people in Chicago and the suburbs.
Between 2000 and 2010, officials have reversed the river four times, during other severe storms. The Chicago Tribune notes that today is "the first time since July 2011 that district engineers redirected rain-swollen waterways back into the lake."