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) of the Muddy River into the tidal Charles was much wider. It formed the eastern Brookline border with Boston and Roxbury (depending on the year), from Brookline's incorporation in 1705 until Boston's annexation of Allston–Brighton in 1873. The present form of the river and surrounding parks was created by the Emerald Necklace project, between 1880 and 1900. Under the direction of designer Frederick Law Olmsted, the project reclaimed marshland, creating sculpted and planted riverbanks. The Muddy River is mentioned by John Winthrop, in his famous "Journal of John Winthrop," as the site of an unidentified flying object in March 1638