Diverting the Lake Michigan Watershed: A Brief History of the Chicago Canal System

Last week I attended the very thought provoking event called Water: The New Oil? The featured speaker was Debra Shore, a Commissioner at the Metropolitan Water Reclamation District. Her presentation provided a very comprehensive overview of the unique geography of the Chicago metropolitan area. But what I found to be particularly fascinating was how one simple canal has substantially impacted Lake Michigan and our water supply.

I spoke with Debra briefly after the event, and she was kind enough to have her office forward some of the presentation graphics for this posting. So let’s take a look at the unique geography of Chicago and how the modification of this geography has affected what’s known as the Lake Michigan Watershed.

Around 15,000 years ago, the entire Great Lakes basin was covered in glacial ice more than a mile thick in some areas. As this massive ice shelf receded, it carved out countless fissures and valleys, redistributing vast amounts of soil in the process.

One of the local by products of this glacial retreat was the formation of the subcontinental divide, a ridge of raised earth that separated the Des Plaines river basin from the Chicago River and Calumet River basins. Modern day Harlem Avenue roughly runs over this raised section of terra firma.

Historically, the Des Plaines River drained westward into the Illinois and Mississippi rivers, eventually reaching the Gulf of Mexico. By contrast, the Chicago and Calumet rivers drained into Lake Michigan.

An important item to note here is that any rain that fell to the east of the subcontinental divide served as a significant source of fresh water replenishment for Lake Michigan.

Up until 1900, the Chicago River was the city’s defacto “sewage system.” With human and industrial waste being expelled directly into Lake Michigan, the mouth of the Chicago River was a literal cesspool. And the now prime real estate known as Streeterville was a disease-ridden squatters’ camp nicknamed “The Sands.” In fact, the Chicago lakefront was so polluted that the only way to effectively provide clean drinking water was to build the water intake cribs two or more miles out in the distance. But by the late 1800’s, even that wasn’t far enough away.

So the city planners at the time came up with a radical solution – namely, to reverse the flow of the Chicago River by creating a canal from the Chicago River to the Des Plaines River. And in 1900, the Chicago Sanitary and Ship Canal was completed:

In order to do this, however, they had to create a breach in the subcontinental divide and disrupt an ecosystem that had developed and existed for thousands of years.

Before the Canal

After the Canal

There are two things to note here:

1) Fresh water sources (i.e. rain water) that used to drain eastward into Lake Michigan via this watershed now instead flow westward

Here’s a graphic which illustrates the diverted portion of the watershed that now no longer replenishes Lake Michigan:

2) Lake Michigan itself is now draining into the Gulf of Mexico

Bottom line, since 1967, when more accurate measurements began, it is estimated that over 30 trillion gallons of fresh water have been taken away from Lake Michigan.

The key point here is that we’re witnessing Newton’s Law on a grand scale. Namely, to every action there is an equal and opposite reaction. When you radically alter an existing system in nature – even if it is for a seemingly noble purpose – you’re going to get a radical reaction somewhere down the line. And it may not be an instant and obvious one, either.

So keep all this in mind whenever you look out on Lake Michigan. And don’t let its vastness mislead you. Remember – it may be big, but that doesn’t mean it’s infallible.