The Chicago Portage is a narrow strip of land separating the Des Plaines River (which drains to the Mississippi River and the Gulf of Mexico) and Lake Michigan (connecting to the Atlantic Ocean via the St. Lawrence Seaway).

This continental divide was breached in 1848 by the Illinois and Michigan Canal, later replaced by the larger Chicago Sanitary and Ship Canal in 1900.

The canal allowed for diverting water from the Chicago River, reversing its flow so that now it drains away from Lake Michigan.