DOWNTOWN — At its beginning headwaters deep into northern Lake County, the Chicago River is no deeper than a few inches and just 1½ feet wide.
Chicago's famous river begins with three forks that start 40 miles north of Downtown. The most northern fork starts in Park City, Ill., as water flowing over and through the soil until it channelizes at the headwaters, according to John Quail, director of watershed planning for Friends of the Chicago River.
"It's fed by runoff, like a mountain stream without the mountain," Quail said.
The most northern fork flows south through the North Shore into the Chicago Botanic Garden before becoming part of the Skokie Lagoon. That branch joins the Middle Fork in Watersmeet Woods in Northfield Township.
The Middle Fork starts with runoff water from a Lake County residential development in Abbott Park, Ill., while the West Fork begins in a farm field in Lincolnshire, Ill., according to Friends of the Chicago River.
Those two waterways join the West Fork to form the river's North Branch at Chick Evans Golf Course in Morton Grove before heading into the city. At the golf course, the North Branch is 30 feet wide and 6 feet deep, Quail said.
From there, the river heads into the city. The North Branch becomes the South Branch at Wolf Point, where it flows south to the Chicago Sanitary and Ship Canal — and eventually to the Gulf of Mexico.
Also at Wolf Point, the river connects to what's known as its "Main Stem" — the best-known section of the river that cuts through Downtown along Wacker Drive and to Navy Pier.
"Most people only think of the Downtown portion as the Chicago River," Quail said. "People are surprised that the river starts so far north, and the people that live near the headwaters are surprised to hear the small streams that they see are the same river they see Downtown."
Map of Chicago waterways, including the three forks that make up the North Branch of the Chicago River. [U.S. Army Corps of Engineers]
Quail said the Chicago River evolved with the landscape over thousands of years after the last glaciers left the Chicago area. Before Chicago was settled, the river's branches and forks were part "meandering, muddy prairie stream" and at times "probably indistinguishable from the swampy/wetland conditions it was moving through," Quail said.
"It has been channelized and straightened as the area has developed," Quail said.
In 1900, when the city altered the Chicago River's flow from going into Lake Michigan to diverting out of the city, the most northern forks of the river were not affected, Quinn said.
He said the headwaters have been most affected by development.
"As we pave over the landscape, more water runs into the river channels that make up the three forks of the North Branch," he said. "Historically these channels held water intermittently based on recent rain, weather, etc. Nowadays they contain flowing water almost all of the time."
Girl Scouts volunteer at the headwaters of the West Fork of the Chicago River. [John Quail]
For more neighborhood news, listen to DNAinfo Radio here.