The Chicago River is 156 miles long, and flows through downtown Chicago. The northernmost branches of the river are the West Fork, the East Fork (a.k.a. Skokie River) and the Middle Fork, which join into the North Branch at Morton Grove, Illinois. The North Branch meets up with the Main Branch of the Chicago River at Kinzie Street in Chicago. The Main Branch flows due West from Lake Michigan, past the Wrigley Building and the Merchandise Mart. The Chicago River has 45 movable bridges spanning it, down from a one-time high of 52 bridges. These bridges include several different types, including trunnion bascule, scherzer rolling lift, swing bridges and vertical lift bridges.
In the 1770s, Jean Baptiste Point du Sable built his farm on the northern bank of the river, the first non-Native American settlement of Chicago, and early in the next century, Fort Dearborn was built on the southern bank of the river
Originally, the river flowed into Lake Michigan, which allowed sewage and other pollution into the clean-water source for Chicago. This contributed to several public health issues including a major cholera epidemic. In 1871 much of the flow was diverted across the Chicago Portage into the Illinois and Michigan Canal. In 1900, the Sanitary District of Chicago completely reversed the flow of the river using a series of canal locks and caused the river to flow into the newly completed Chicago Sanitary and Ship Canal. Before this time the Chicago River was known by many local residents of Chicago as "the stinking river" because of the massive amounts of sewage and pollution which poured into the river from Chicago's booming industrial economy.
Every year on St. Patrick's Day, the river is dyed green. The Pipefitters Union uses fluorescein dye which can also be used to study moving water. While in 1962, 100 pounds (45 kg) of dye were used, more recently the amount has been decreased to about 40 pounds.