Chicago

Environment

Two bodies of water have been central to the history and development of the city of Chicago—the Chicago River and Lake Michigan, the third largest of the Great Lakes and the only one completely within the United States. The southwestern shore borders an urban area that includes not only Chicago, but also Milwaukee, Wisconsin, and Gary, Indiana. The concentration of industrialization has led to growing pollution problems.

The Chicago River formerly flowed into Lake Michigan, but its course was reversed, because of pollution, in 1900. In the waning years of the twentieth century, significant efforts were made to clean up the river, which had suffered from the effects of unhampered industrialization since the nineteenth century. The Chicago River became a repository of refuse from the slaughterhouse industry and other forms of industrial pollution. By 1999, over 50 species of fish—including salmon, carp, and perch—returned to the river's waters, and the Friends of the Chicago River began to lead walking tours along the riverfront.

Encircling the city along its northern, western and southern boundaries, the Cook County Forest Preserves cover 66,746 acres, providing woodlands, open spaces, and recreational facilities. About five percent of the preserves belong to the Illinois Nature Preserve system, which protects the natural habitats of endangered species and other animals.