The Calumet River is a system of heavily 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.

Gary is a city in Lake County, Indiana, United States. As of the 2020 census the city's population was 69,093, making it Indiana's ninth-most populous city. The city has been historically dominated by major industrial activity and is home to U.S. Steel's Gary Works, the largest steel mill complex in North America. Gary is located along the southern shore of Lake Michigan about 25 miles (40 km) southeast of downtown Chicago. The city is the western gateway to the Indiana Dunes National Park, and is within the Chicago metropolitan area.