The
Illinois River is a principal tributary of the
Mississippi River, approximately long, in the
U.S. state of
Illinois. The river drains a large section of central Illinois, with a drainage basin of .
The river was important among
Native Americans and early
French traders as the principal water route connecting the
Great Lakes with the Mississippi. The French colonial settlements along the river formed the heart of the area known as the
Illinois Country. After the construction of the
Illinois and Michigan Canal and the
Hennepin Canal in the 19th century, the river's role as link between
Lake Michigan and the Mississippi was extended into the era of modern industrial shipping.
Hydrography
The Illinois River is formed by the confluence of the
Kankakee and
Des Plaines rivers in eastern
Grundy County, approximately 10 miles (16 km) southwest of
Joliet. It flows west across northern Illinois, passing
Morris and
Ottawa, where it is joined by the
Mazon River and
Fox River. At
LaSalle, it is joined by the
Vermilion River, then flows west past
Peru, and
Spring Valley. In southeastern
Bureau County it turns south at an area known as the "Great Bend," flowing southwest across western Illinois, past
Lacon and downtown
Peoria, the chief city on the river.
South of Peoria it is joined by the
Mackinaw River and then passes through the
Chautauqua National Wildlife Refuge. Opposite
Havana, it is joined by the
Spoon River, and across from
Browning, it is joined by the
Sangamon River. The
La Moine River flows into it approximately 5 miles (8 km) southwest of
Beardstown.
Near its confluence with the
La Moine River, it turns south, flowing roughly parallel with the Mississippi across southwestern Illinois. It is joined by
Macoupin Creek on the border between
Greene and
Jersey counties, approximately 15 miles (24 km) upstream from its confluence with the Mississippi.
For the last 20 miles (32 km) of its course, it is separated from the Mississippi by only 5 miles (8 km), a peninsula that comprises
Calhoun County. It joins the Mississippi near
Grafton, approximately 25 miles (40 km) northwest of downtown
St. Louis and about 20 miles (32 km) upstream from the confluence of the Missouri and the Mississippi.
Geology
South of
Hennepin, the Illinois River is following the ancient channel of the
Mississippi River. The
Illinoian Stage, about 300,000 to 132,000 years ago, blocked the Mississippi near
Rock Island, diverting it into its present channel. After the glacier melted, the Illinois River flowed into the ancient channel. The
Hennepin Canal roughly follows the ancient channel of the Mississippi upstream of Rock Island.
The modern channel of the Illinois River was shaped in a matter of days by the Kankakee Torrent. During the melting of the
Wisconsin Glacier about 10,000 years ago, a lake formed in present-day Indiana, comparable to one of the modern
Great Lakes. The lake formed behind the terminal moraine of a substage of that glacier. Melting ice to the north eventually raised the level of the lake so that it overtopped the moraine. The dam burst, and the entire volume of the lake was released in a very short time, perhaps a few days.
Because of the manner of its formation, the Illinois River runs through a deep canyon with many rock formations. It has an "underutilised channel," one far larger than would be needed to contain any conceivable flow in modern times.
Image:Flooding along the Illinois River (Before).jpg|Late October 2009 (before the flood).
Image:Flooding along the Illinois River (After).jpg|Early November 2009 (during the flood).
History
The Illinois River as mapped in 1718, modern Illinois state highlighted.
The Illinois River valley was one of the strongholds of the
Illinois Confederation of
Native Americans. The French first met the natives here in 1673. The first
European settlement in the state of Illinois was the
Jesuit mission founded in 1675 by Father
Jacques Marquette on the banks of the Illinois at
Starved Rock. In 1680,
René-Robert Cavelier, Sieur de La Salle built the first fort in Illinois, Ft. St. Louis, at Starved Rock. Later it was relocated to the present site of Creve Coeur, near Peoria, where the Jesuits relocated.
Modern use
River tow leaving the Starved Rock Lock headed down river.
From 1905 to 1915, more freshwater fish were harvested from the Illinois than from any other river in the United States except for the
Columbia. The river was once a major source of
mussels for the shell button industry.
Overfishing, habitat loss from heavy
siltation and
pollution have eliminated most commercial fishing except for a small mussel harvest to provide shells to seed
pearl oysters overseas. It is commercially fished downstream of the Rt. 89 bridge at Spring Valley. The river is still an important sports fishing resource with a world-class
sauger fishery.
The Illinois forms part of a modern waterway that connects the
Great Lakes at
Chicago to the Mississippi River. The waterway was originally established by the building of the
Illinois and Michigan Canal that connected the Illinois River to the
Chicago River. When the
Sanitary District of Chicago later
reversed the flow of the Chicago River, the pollution and
sewage of the city of Chicago flowed down into the Illinois River. The Illinois and Michigan Canal has since been replaced by the
Illinois Waterway, including the
Chicago Sanitary and Ship Canal. River traffic and flood control is managed by eight locks and dams operated by the Army Corps of Engineers. Currently all locks and dams are closed to visitors for security reason except the Starved Rock Visitor Center, which offers an excellent interpretation of the entire system. The waterway is heavily used by barges' transporting bulk goods such as grain and oil. It is used in the summer and early fall by tourists in pleasure boats cruising the
Great Loop. The Illinois River is an important part of the
Great Loop, the circumnavigation of Eastern North America by water.
The City of
Peoria is developing a long-term plan to reduce
combined sewer overflows to the Illinois River, as required by the
U.S. Environmental Protection Agency and the
Illinois Environmental Protection Agency. During dry weather, sewage flows safely through the city's sewers to the Greater Peoria Sanitation District
wastewater treatment plant. However, about 28 times a year, melting snow or rainwater can overwhelm the sewers, causing untreated sewage to overflow into the Illinois River. Peoria was required to examine the sewer overflows and prepare a long-term control plan to meet
Clean Water Act requirements and protect the Illinois River. The city had to submit its plan by December 2008 to U.S. EPA and Illinois EPA.
Cities and towns
See also
