Chicago Area Waterway System in the context of North Shore Channel

The Illinois Waterway system consists of 336 miles (541 km) of navigable water from the mouth of the Calumet River at Chicago to the mouth of the Illinois River at Grafton, Illinois. Based primarily on the Illinois River, it is a system of rivers, lakes, and canals that provide a commercial shipping connection from the Great Lakes to the Gulf of Mexico via the Illinois and Mississippi rivers.

The Illinois and Michigan Canal (I&M) opened in 1848. In 1900, the Chicago Sanitary and Ship Canal replaced the I&M and reversed the flow of the Chicago River so it no longer flowed into Lake Michigan. The United States Army Corps of Engineers maintains a 9-foot-deep (2.7 m) navigation channel in the waterway. The waterway's complex northern section is referred to in various contexts for study and management as the Chicago Area Waterway System (CAWS).

The Calumet River is a system of industrialized rivers and canals in the region between the south side of Chicago, Illinois, and the city of Gary, Indiana. Historically, the Little Calumet River and the Grand Calumet River were one, the former flowing west from Indiana into Illinois, then turning back east to its mouth at Lake Michigan at Marquette Park in Gary. Now the system is part of the Chicago Area Waterway System and through the use of locks flows away from Lake Michigan to the Cal-Sag Channel.

The Calumet-Saganashkee Channel, usually shortened to the Cal-Sag Channel, is a 16-mile-long (26 km) drainage and shipping canal in southern Cook County, Illinois, operated by the Metropolitan Water Reclamation District of Greater Chicago (MWRD). A component of the Chicago Area Waterway System, it connects the Little Calumet River at its eastern end to the Chicago Sanitary and Ship Canal at its western end.

The Cal-Sag Channel is utilized for inland shipping, recreational boating and drainage purposes in what was an active zone of heavy industry in the Far Southeast Side neighborhoods of the city of Chicago and adjacent suburbs. As a drainage channel, it is used as a conduit for treated effluent wastewater from southern Cook County, including the Chicago-area Deep Tunnel Project, into the Illinois Waterway. It is also used in the summertime by pleasure crafts.

The Chicago Harbor Lock, also known as the Chicago River & Harbor Controlling Works, is a stop lock and dam located within the Chicago Harbor in Chicago, Illinois, at the mouth of the Chicago River. It is a component of the Chicago Area Waterway System, and is used to control water diversion from Lake Michigan into the river and for navigation.

Thomas J. O'Brien Lock & Dam is a stop lock in the Hegewisch neighborhood on the South Side of Chicago at the confluence of the Grand Calumet River and Little Calumet River, which form the Calumet River. It is a component of the Chicago Area Waterway System (CAWS), which is, itself, a part of the Illinois Waterway, which links the Mississippi River and the Great Lakes.

The Lock & Dam is named for Thomas J. O’Brien, who was a U.S. Representative for the 6th District of Illinois from 1933 to 1938 and again from 1943 to 1964.