Illinois River 20 miles (32 km) of its course, the Illinois is separated from the Mississippi River by only about five miles, by a peninsula of land that makes up Calhoun County. The Illinois joins the Mississippi near Grafton, approximately 25 miles (40 km) northwest of downtown St. Louis and about 20 miles upstream from the confluence of the Missouri River and the Mississippi. 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
Muddy River (Massachusetts) flows through a conduit under Route 9 and into a narrow park called the Riverway, from which it flows through three culverts: the Riverway Culvert, the Brookline Avenue Culvert, and the Avenue Louis Pasteur Culvert. The Muddy River continues from the Fens toward its connection with the Charles River via the Charlesgate area, running through a stone-paved channel surrounded by a narrow strip of parklands. In a series of stone bridges and tunnels, it passes under Boylston Street, Massachusetts Turnpike, Commonwealth Avenue, Storrow Drive, and a series of elevated connecting ramps (the Bowker Overpass). In its natural state, the outlet