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The Chicago River is 156 miles (251 km) long, and flows through downtown Chicago. 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 dying it green on St. Patrick's Day.

Contents 1 Geography 2 Ecology 3 History 3.1 Reversing the flow 3.2 Chicago Flood 3.3 St. Patrick's Day 4 Bridges 5 See also 6 References 7 External links

The northernmost branches of the river are 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. 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, before turning south.

The Chicago River has been highly affected by the industrial and residential areas around with attendant changes to the quality of the water and riverbanks. Several species of warmwater fish are known to occur in the river including largemouth and smallmouth bass, rock bass, crappie, bluegill, catfish and carp. The river also has a large population of crayfish. The South Fork of the Main (South) Branch, which was the primary sewer for the Union Stock Yards and the meatpacking industry, was once so polluted that it became known as Bubbly Creek.^[1] Illinois has issued advisories regarding eating fish from the river due to PCB and mercury contamination, including a "do not eat" advisory for carp more than 12" long [1]. There are concerns that silver carp and bighead carp, now invasive species in the Mississippi and Illinois Rivers, may reach the Great Lakes through the Chicago River [2].

In the 1770s, Jean Baptiste Pointe du Sable built his farm on the northern bank of the river near Wolf Point, 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. In 1900 the river's flow was reversed in order to keep Lake Michigan clean. In 1915, the Eastland, an excursion boat docked at the Clark Street bridge, rolled over, killing 812 passengers. In 1928, the South Branch of the Chicago River between Polk and 18th Street was straightened and moved ¼ miles (400 m) west to make room for a railroad terminal.

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 some problems with typhoid [3]. 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, then headed by Rudolph Hering, 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. Up through the 1980s, the river was quite dirty and often filled with garbage; however, during the 1990s, it underwent extensive cleaning as part of an effort at beautification by Chicago Mayor Richard M. Daley.

Recently, researchers at the University of Illinois at Urbana-Champaign created a three-dimensional, hydrodynamic simulation of the Chicago River, which suggested that density currents are the cause of an observed bi-directional wintertime flow in the river. At the surface, the river flows east to west, away from Lake Michigan, as expected. But deep below, near the riverbed, water travels west to east, toward the lake [4].

All outflows from the Great Lakes basin are regulated by a joint U.S.-Canadian commission and the outflow through the Chicago River is set under a U.S. Supreme Court decision (1967, modified 1980 and 1997). The city of Chicago is allowed to remove 3200 cubic feet per second (91 m³/s) of water from the Great Lakes system; about half of this, 1 billion US gallons a day (44 m³/s), is sent down the Chicago River, while the rest is used for drinking water [5]. In late 2005 the Alliance for the Great Lakes proposed separating the Great Lakes and Mississippi River basins [6]. Presumably this plan would restore the Chicago River's original natural flow.

In 1992 the Chicago Flood occurred when a pile driven into the river punctured a hole in the wall of the long abandoned tunnel of the Chicago Tunnel Company near Kinzie Street. Most of the 60-mile (97 km) network of underground freight railway, which encompasses much of downtown, was eventually flooded along with the lower levels of buildings it once serviced and attached underground shops and pedestrian ways.

Every year on St. Patrick's Day, the river is dyed green.

Bill King, the administrator of Chicago's St. Patrick's Day committee, stated that the idea of dyeing the Chicago River green originally came about by accident when a group of plumbers were using green dye to trace illegal substances that were polluting the river.

The chemical used during the 1960s to turn the river green was a fluorescent dye. This dye is not allowed anymore because the EPA (Environmental Protection Agency) outlawed the use of the chemical that was proven to be harmful to the river. The secret ingredients used to dye the river green today are safe and are not harmful to the thousands of goldfish that make up a large percentage of the river's fish population.

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.

The following bascule bridges cross the river (and its south branch) into the Chicago Loop:

• Harrison Street Bridge (1960)
• Congress Parkway Bridge (1954)
• Van Buren Street Bridge (1956)
• Jackson Boulevard Bridge (1916)
• Adams Street Bridge (1927)
• Monroe Street Bridge (1919)
• Madison Street Bridge (1922)
• Washington Street Bridge (1913)
• Randolph Street Bridge (1984)
• Lake Street Bridge (Chicago) (1915)
• Franklin Street Bridge (1919)
• Wells Street Bridge (1922)
• La Salle Street Bridge (1928)
• Clark Street Bridge (1929)
• Dearborn Street Bridge (1962)
• State Street Bridge (1948)
• Wabash Avenue Bridge (1930)
• Michigan Avenue Bridge (1920)
• Columbus Drive Bridge (1982)
• Lake Shore Drive Bridge (originally known as the Outerlink Drive Bridge) (1936)

• Chicago
• List of Illinois rivers
• Bascule bridges

• Friends of the Chicago River

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