<P> In 1848, the Illinois and Michigan canal linked the river to the Illinois River and the Mississippi Valley across the Chicago Portage . This canal was the farthest west, and the last, of a series of United States' government land grant canals . It provided the only water route from New York City to New Orleans through the county's interior and Chicago . </P> <P> During the last ice age, the area that became Chicago was covered by Lake Chicago, which drained south into the Mississippi Valley . As the ice and water retreated, a short 12 - to - 14 - foot (3.7 to 4.3 m) ridge was exposed about a mile inland, which generally separated the Great Lakes' watershed from the Mississippi Valley, except in times of heavy precipitation or when winter ice flows prevented drainage . By the time Europeans arrived, the Chicago River flowed sluggishly into Lake Michigan from Chicago's flat plain . As Chicago grew, this allowed sewage and other pollution into the clean - water source for the city, contributing to several public health problems, like typhoid fever . Starting in 1848, much of the Chicago River's flow was also diverted across the Chicago Portage into the Illinois and Michigan Canal . In 1871, the old canal was deepened in an attempt to completely reverse the river's flow but the reversal of the river only lasted one season . </P> <P> Finally, in 1900, the Sanitary District of Chicago, then headed by William Boldenweck, completely reversed the flow of the Main Stem and South Branch of the river using a series of canal locks, increasing the river's flow from Lake Michigan and causing it to empty into the newly completed Chicago Sanitary and Ship Canal . In 1999, this system was named a "Civil Engineering Monument of the Millennium" by the American Society of Civil Engineers (ASCE). Before this time, the Chicago River was known by many local residents of Chicago as "the stinking river" because of the massive amounts of sewage and pollution that poured into the river from Chicago's booming industrial economy . </P> <P> Through the 1980s, the river was quite dirty and often filled with garbage; however, during the 1990s, it underwent extensive cleaning as part of an effort at beautification by Chicago Mayor Richard M. Daley . </P>

How did they change the flow of the chicago river
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