The Chicago River watershed is formed of the North and South Branches of the Chicago River. The North Branch Chicago River is an urban river. It originates as three forks: the fourteen mile West Fork, twenty-four mile Middle Fork (also known as the West Skokie), and the seventeen mile Skokie River. The South Branch flows into the Chicago Sanitary and Ship Canal where it is diverted westward joining with the Des Plaines River as a tributary of the Illinois River.
The watershed has a drainage area of approximately 360 square miles (233,600 acres).
