The Chicago River is a river that runs 156 miles (251 km) and flows through Chicago, including Downtown Chicago, also known as the Chicago Loop. Though not especially long, the river is notable for the 19th century civil engineering feats that directed its flow south, away from Lake Michigan, into which it previously emptied, and towards the Mississippi River basin. This was done for reasons of sanitation. The river is also noted for the local custom of dyeing it green on St. Patrick's Day.
Originally, the river flowed into Lake Michigan. Its course jogged southward from the present river to avoid a baymouth bar, entering the lake at about the level of present day Madison Street. Today, the Main Stem of the Chicago River flows due west from Lake Michigan, past the Wrigley Building and the Merchandise Mart to Kinzie Street, where it meets the North Branch of the river. The North Branch is formed by the West Fork, the East Fork (also known as the Skokie River) and the Middle Fork, which join into the North Branch at Morton Grove, Illinois. From downtown, the river flows south along the South Branch, and into the Illinois and Michigan Canal and Chicago Sanitary and Ship Canal. From there, the water flows into the Des Plaines River and eventually reaches the Gulf of Mexico.