Undercurrents: beneath the obvious

December 2, 2006

A Brief History of the Chicago Diversion

The Chicago diversion is the largest and best known out-of-basin diversion of the Great Lakes.

In 1848, the Illinois-Michigan Canal was opened to shipping traffic. This resulted in the diversion of 240 million liters per day (mld) or 64.6 million gallons per day (mgd) of water from Lake Michigan at Chicago through the Chicago and Illinois Rivers to the Mississippi River.

At that time Chicago’s sewage flushed into the slowly moving, almost stagnant Chicago River and thence into Lake Michigan — the source of Chicago’s drinking water. In 1885, 90,000 people died in Chicago from cholera as a result of this situation; this was over 10% of the city’s population.

Because of this disaster, the Drainage and Water Supply Commission and the Sanitary District of Chicago were formed. The commission built a new channel and control structures to reverse the flow of the Chicago and Calumet Rivers so that sewage from Chicago would flow through the Illinois River to the Mississippi. The canal was completed in 1900.

During the 1920’s, the Chicago diversion was as high as 24,000 mld (6,463 mgd). In 1967, the U.S. Supreme Court limited the diversion to 7,600 mld (2,068 mgd), the level it is supposed to be at today.

The Chicago diversion has three components. The first component, 62 percent of the diversion, provides the water supply for the 5.7 million residents of northeast Illinois. The second component is a direct diversion from Lake Michigan into the Illinois River and Canal system for safe navigation and to increase flow in order to improve water quality in the Chicago area. The third component, 20 percent of the allowed diversion, is storm water runoff that would have flowed into the Chicago River and from there into Lake Michigan, but which now flows the opposite direction into the Mississippi watershed.

The level of flows at this diversion has always been a controversial topic because it is the largest diversion out of the Great Lakes Basin and always threatens to increase. The current allocation of 7,600 mld (2,068 mgd) averaged over a forty-year period was established by a U.S. Supreme Court decree issued in 1967 and amended in 1980.

In 1995, a dispute arose between Michigan and Illinois because approximately 740 mld (200 mgd) more water was being diverted from Lake Michigan through the Chicago diversion than allowed by the court decree. Illinois argued that a “paper change rather than a physical change” in the diversion had occurred. The state said new, more accurate velocity flow meters were being used to measure the diversion and that canal locks maintained by the U.S. Army Corps of Engineers were leaking. Michigan argued that Illinois “can’t pretend that one number is another.”

The federal government and the eight Great Lakes states took this dispute to mediation. Illinois and Michigan requested that the Army Corps of Engineers be granted authority under the Water Resources Development Act to proceed with necessary repairs to eliminate leakage through the locks.

In October 1996, the concerned parties came to an agreement in which Illinois agreed to reduce the out take of water from Lake Michigan to the amount set in the 1967 and 1980 court decree. In return the eight Great Lakes states agreed not to take legal action over the withdrawal violations that had already occurred.

Today, nearly 7 million northeastern Illinois residents live outside the lake’s drainage basin – more than half of the state’s total population – yet are fortunate enough to have access to lake water because of this diversion.

And so the continuing good fortune of Chicago suburbs attracts the covetous eyes of southeastern Wisconsin officials.

Source: The Fate of the Great Lakes: Sustaining or Draining the Sweetwater Seas?



  1. I came across your site searching for answers to the question of the incredibly low water levels in Lakes Huron and Superior these days (April 2007). You provide a tremendous amount of information which I found enlightening and in some cases disturbing. May I suggest you edit part of your title line above to read “The Great Lakes……….make up 95% of the fresh water in North America….” not the “United States”. The Great Lakes are international waters shared by two great democracies. It is important to keep this in mind.

    Comment by Robert Askin — April 27, 2007 @ 7:21 pm | Reply

  2. Robert, thanks for the comment and notice the change in the title line.

    Comment by nemo — April 27, 2007 @ 9:03 pm | Reply

  3. An interesting article. Water is indeed essential for life. So we have to use it very wisely. Inform people that we should not waste any water.

    Comment by Frits Koelers — February 26, 2008 @ 6:14 am | Reply

  4. I moved to a canal with access to Lake St Clair in 1996. How ironic that the water levels started to drastically drop at the same time that the dispute over the diversion began. Water levels are still extremely low in Lake St Clair and it is my belief that the current flooding conditions hitting the midwest is being caused by these diversions. We need to STOP these diversions and let nature take its course!

    Comment by Dianne Miller — June 17, 2008 @ 7:06 am | Reply

  5. Actually, to address Dianne’s point, Canada’s big water diversions *into* the Great Lakes (at Thunder Bay) are far larger than America’s diversions *out of* the Lakes. I don’t deny that the Chicago diversion has immense ecological effects — and, in fact, have advocated returning the Chicago River to its natural easterly flow — but it’s not related to low levels in St. Clair: the disputed amount equals ~0.2% of the annual flow past Detroit.

    Chicago also has nothing to do with flooding in Cedar Rapids. The most destructive floods in the Midwest were all well upstream of St. Louis (well, Grafton), where the Illinois River (which carries Chicago’s wastewater) joins the Mississippi.

    Comment by payton — June 21, 2008 @ 12:37 am | Reply

  6. >May I suggest you edit part of your title line above to read “The Great Lakes……….make up 95% of the fresh
    >water in North America….” not the “United States”. The Great Lakes are international waters shared by two
    >great democracies.

    Although it’s been taken out of the original post in it’s entirety, it would be good to note that the percentage changes if the geographic area is changed.

    The Great Lakes contain 95% of the fresh water in the United States. http://www.epa.gov/25water/everybody.html. I believe that’s just the U.S. “share” of the water.

    Because of Canada’s very extensive and large system of lakes — just take a look on a map of the line of very large if not great lakes stretching northwest of Superior, as well as the numerous lakes eastward through Quebec, when you change to “North America” and include all the water of the lakes, the percentage drops to 84%.

    I know this is an update on an old post, but a google of the Chicago Diversion returns this high in it’s results (that’s how I stumbled on it).

    Comment by Matt from CT — May 8, 2010 @ 7:08 pm | Reply

  7. This was the reference for the 84%: http://www.epa.gov/glnpo/basicinfo.html

    Comment by Matt from CT — May 8, 2010 @ 7:09 pm | Reply

  8. I like the post and perhaps a modification might be in order given the planet warming situation and resulting increased lakes evaporation each summer.
    I hope I am correct in concluding “mgd” is million gallons perday. Right?

    Comment by as above — March 23, 2012 @ 10:42 am | Reply

  9. I’m not sure exactly why but this website is loading extremely slow for me. Is anyone else having this problem or is it a issue on my end? I’ll check back later on and
    see if the problem still exists.

    Comment by Manjushri Chauhan — October 2, 2012 @ 5:58 am | Reply

  10. […] all manner of waterborne illnesses that were infecting our drinking water; this is the so-called “Chicago Diversion.” The reversal effort could be undone in the coming months as drought conditions may lower Lake […]

    Pingback by Henry Henderson: Will the Chicago River Change Course and Flow Back Into the Great Lakes? | Elm River Free Press — December 24, 2012 @ 4:47 pm | Reply

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