Reversing the Chicago River, Again

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I recently attended a panel discussion, hosted by the Chicago Council on Science and Technology, about the relationship between water and Chicago. I had gone into this seminar expecting to hear mostly about Lake Michigan, but there was a surprising focal point of the discussion: the Chicago River.

Most Chicagoans have heard about the legendary reversal of the flow of the Chicago River. Once planned and approved, this was an eight-year long project that took thousands of people to execute. As crazy as it sounds, it was a human intervention bred of necessity.

Back in the 1800s, sewage from the growing city of Chicago was dumped into the river, which at the time flowed into Lake Michigan. There, the sewage was diluted and the lake's current eventually swept it away. Since the concentration of pollutants was highest at the mouth of the river, where it emptied into Lake Michigan, the city's drinking water was collected from further offshore.

However, this dilution process was much too slow to adequately deal with the waste of the ever-growing population, and during large storms sewage would find its way into the city's drinking supply. In addition, the heavily polluted river flowed through a densely populated area, which increased the risk of contracting waterborne diseases such as cholera or typhoid. Residents of Chicago were essentially living alongside an open sewer system and naturally, they weren’t too pleased about it.

Faced with such problems, city officials decided to construct water passages, most notably the Sanitary and Ship Canal, to reverse the flow of the Chicago River. Doing so meant that cleaner water from Lake Michigan would flow into the Chicago River, diluting its pollutants, and washing it away from the city into the Des Plaines River. Eventually, as water reclamation plants were constructed around the city, the river became even less polluted and the pollutants being added to the river became increasingly regulated.

Today, we have much more sophisticated water treatment. But now, new environmental problems have arisen regarding the Chicago River. The reversal of the Chicago River through Sanitary and Ship Canal also connected Lake Michigan to the Mississippi River, and the Upper Mississippi to the Great Lakes watershed. As a result, organisms have been able to migrate between these two areas, often causing detrimental effects to their non-native environments. You’ve probably heard of the havoc wreaked by Asian carp and zebra mussels. If left unchecked, these and other invasive and nuisance species could ruin biodiversity, damage infrastructure, and end up costing Chicago and other cities millions of dollars.

Another concern, although not as prominent, is the potential of a declining volume of Lake Michigan. With the reversal of the Chicago River, 3,200 cubic feet per second a day is now leaving the lake though that waterway. Chicago is located right on the continental divide that separates the Great Lakes and Mississippi watersheds. Before the reversal of the river, rainfall to the west of the divide would flow into the Des Plaines River and out to the Mississippi, and rainfall to the east would flow into the Chicago River and replenish Lake Michigan. Now, rainfall to the east that ends up in the Chicago River flows in the opposite direction: towards the Mississippi.

Although there's no immediate danger of Lake Michigan being reduced to a puddle, if climate change trends continue we could see a noticeable decrease in water level many years from now.

So, what’s the solution? A new reversal of the Chicago River might be the answer to these and other water concerns in the Second City. By restoring the river to its natural flow, we may be able to halt the progression of invasive species from the east. Not only that, but a reversal of the river could greatly decrease the risk of reduced lake water levels in the future. Such a project would be very costly, but in the long run may be worth it.

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