The Chicago Sanitary and Ship Canal, historically known as the Chicago Drainage Canal, is the only shipping link between the Great Lakes (specifically Lake Michigan by the Chicago River) with the Mississippi River system, by way of the Illinois and Des Plaines Rivers. The canal also carries Chicago's treated sewage into the Des Plaines River. Before completion of the canal in 1900, the sewage of Chicago was dumped into Lake Michigan, the city's drinking water supply. The canal is part of the Chicago Wastewater System, operated by the Metropolitan Water Reclamation District of Greater Chicago. The system has been named a Civil Engineering Monument of the Millennium by the American Society of Civil Engineers (ASCE). The Chicago Sanitary and Ship Canal is 28 miles (45 kilometers) long, 202 feet (62 m) wide, and 24 feet (7.3 m) deep. Prior to its construction, the Illinois and Michigan Canal connected the same waterways for boat travel.
The canal, linking the south branch of the Chicago River to the Des Plaines River at Lockport, was completed in 1900. An extension from 1903-1907 allowed for the canal to extend to Joliet. The rate of flow is controlled by the Lockport Powerhouse, sluice gates at Chicago Harbor and at the O'Brien Lock in the Calumet River, and also by pumps at Wilmette Harbor. Two more canals were later built to add to the system: The North Shore Channel in 1910, and the Cal-Sag Channel in 1922.
Construction of the Ship and Sanitary Canal was the largest earth-moving operation that had been undertaken in North America up to that time. It was also notable for training a generation of engineers, many of whom later worked on the Panama Canal.
There is some dispute over how much water is actually being diverted by the canal. Recently, researchers at the University of Illinois at Urbana-Champaign built a numerical model of the Chicago River system. The resulting three-dimensional, hydrodynamic simulation successfully proved the likelihood that density currents are causing a bi-directional flow in the Chicago River during winter seasons. At the surface, the river was flowing east to west, away from Lake Michigan, as expected. But deep below, near the riverbed, water was traveling west to east, toward the lake. This flow could be pulling some water out of the Chicago Sanitary and Ship Canal. A summary of the research team's findings was published in the Spring/Summer 2005 edition of the CEE Alumni Association Newsletter