The Great Lakes and the Mighty Mississippi

Two enormous watersheds in central North America

A few weeks ago, I posted an article about watersheds, and in that article, I included a map of the Great Lakes watershed. Upon further inspection of this watershed, I began to notice some interesting things. The watershed of the five Great Lakes lies on the border between Canada and the USA, and four of the lakes are geographically shared between the two countries. The fifth, Lake Michigan, lies solely in the USA.

Upon closer inspection of the Lake Michigan watershed (shown above as the red and dark orange zones), the watersheds seems to disappear on the southwest end of Lake Michigan, near the city of Chicago.

The map below shows a close-up of what the watershed divide looked like near Chicago before 1900. The white dashed line separates the Mississippi River watershed from the Great Lake watershed. This line was less than 10 miles from Lake Michigan (source here) (Note: a line that separates watersheds is called a “divide”)

Back in the 1800s, Chicago was growing as a city (population increased from a few thousand in the 1830s to over 1.6 million by 1900) . In 1848, the Illinois & Michigan Canal was completed. This canal connected the Chicago River to the Illinois River (which drains to the Mississippi River). The canal was 96 miles long and it took 12 years to complete. It also provided a connection from the Great Lakes to the Mississippi River by boat. Sewage from the city of Chicago was dumped into the Chicago River or directly into Lake Michigan. Meanwhile, the city was getting its water from intakes in Lake Michigan.

By the late 1900s, engineers decided to reverse the flow of the southern branch of the Chicago River. This allowed the Chicago River to flow into the Des Plaines River and eventually to the Illinois River and the Mississippi River (and flow away from Lake Michigan). This project resulted in the building of the Chicago Sanitary and Shipping Canal (CSSC). The canal works by taking water from Lake Michigan and discharging it into the Mississippi River watershed. A second canal with a similar function was built to the south (known as the Calumet-Saganashkee Channel). The new map looks like this (source here):

The water network looks very different. The second map shows a water system that allows ships to travel from the Great Lakes down the Mississippi River to the Gulf of Mexico.

This type of canal system is not unique to this area. The Ohio and Erie Canal connects Lake Erie to the Ohio River (which flows to the Mississippi River). After irreparable flood damage in the early 1900s, transportation along this canal ended. The Erie Canal (built in the early 1800s) connects the Hudson River (which flows to the Atlantic Ocean near New York City) to Lake Erie (at Buffalo). Shipping traffic in the Erie Canal declined dramatically when the St. Lawrence Seaway opened in the 1950s.

In the case of the Chicago canals, there has been a number of court cases regarding the taking of water from a trans-national watershed like the Great Lakes and pumping it to another watershed. There are agreements in place to regulate the amount of water that can be removed from Lake Michigan and sent to the Mississippi. For more reading, I recommend Wikipedia (I checked some of the references and some of the links no longer work).

When watersheds are connected, one potential threat is the introduction of invasive species. Zebra mussels have already used canal systems to cross watersheds. Invasive carp species (referred to previously as Asian carp) have been migrating northward through the Mississippi River system since the 1970s. If these carp become prevalent in the Great Lakes, they could reduce the native fish species, thereby affecting the angling industry. Experts are closely monitoring for these invasive species in the area of the Chicago canals.

Some final thoughts:

• Connecting two enormous watersheds like the Great Lakes and the Mississippi has had economic benefits, but there are certainly downsides as well. With the water issues in the US southwest, there’s bound to be conversations about diverting water from the Great Lakes to the desert (here’s one article that suggests this idea)

• Some have proposed re-disconnecting the Chicago River from the Des Plains River, thereby disconnecting the watersheds

• The International Joint Commission (IJC) is a Canada/USA initiative whereby decisions related to water are made jointly between the two countries, with the understanding that each country is affected by the actions of the other with regards to rivers and lakes along the border. Although Lake Michigan is entirely in the USA, it is part of the Great Lakes, which are shared between the two countries.