Evanston residents are fortunate to live at the edge of a stunning natural resource – Lake Michigan.

They appreciate its physical beauty, enjoy the recreational opportunities it offers, and benefit from the fresh drinking water it provides. Indeed, as droughts and water scarcity become more and more prevalent elsewhere, Evanstonians increasingly value their proximity to the Great Lakes – a system that constitutes 20 percent of the world’s fresh surface water and 90 percent of the fresh water supply in the United States.

Protecting this precious resource, however, is an ongoing challenge.

An Engineering Marvel

The first chapter of the story is a familiar one. During the 19th century, untreated sewage from Chicago-area homes and industries discharged into the Chicago River and flowed into Lake Michigan, the primary source of drinking water for area residents. Waterborne diseases in the polluted lake water posed a very serious public health problem.

The solution came in 1889 with the creation of the Sanitary District of Chicago – today the Metropolitan Water Reclamation District (MWRD) – and implementation of a plan to reverse the flow of the Chicago River. The district dug a canal to connect the South Branch of the Chicago River to the Des Plaines River, breaking through the low sub-continental divide just east of the Des Plaines and using fresh water from Lake Michigan to flush the contaminated water into the Des Plaines and ultimately to the Illinois and Mississippi Rivers. 

The North Shore Channel was completed a few years later to carry wastewater from the northern suburbs to the North Branch of the Chicago River. Here, too, the system used water from Lake Michigan to send the sewage downstream.  A third construction project incorporated the Calumet Rivers into the network, now known as the Chicago Area Waterway System (CAWS).

Over time, the district built seven modern water reclamation plants around Cook County; it continues to discharge the now treated wastewater into the CAWS. Sewage from Evanston is treated at the MWRD North Side Water Reclamation Plant at Howard Street and McCormick Boulevard.

Unintended Consequences

In the years since Europeans first settled in the region, more than 180 non-native aquatic species have become established in the Great Lakes, causing economic losses that the Great Lakes Commission estimates at $5.7 billion annually. The primary source of these invasive species has been ballast water discharge from ocean-going ships.  But manmade waterways that connect the Great Lakes basin to other watersheds have provided another important pathway.

The CAWS has already allowed several damaging invasive species to move between the Great Lakes and the Mississippi River basin. Zebra mussels, originally from the Caspian Sea, are altering the food chain and water chemistry of the Great Lakes and wreaking havoc on underwater infrastructure. Discovered in Lake St. Clair near Detroit in 1988, they are now spreading rapidly down the Mississippi River and into connected waterways.

“Invasions” go both ways. Asian carp have been moving up the Mississippi River since the 1990s and pose the newest and most serious threat to the Great Lakes. The fish are highly mobile, reproduce and grow quickly, and consume massive quantities of food, traits that could enable them to displace native species and devastate the region’s sport fishing industry.  

The Army Corps of Engineers has installed a system of electric barriers to prevent the carp from reaching the Great Lakes. In June of this year, however, an Asian carp was found in Lake Calumet, above the electric barrier system and just a few miles from Lake Michigan. Although there is no evidence that a significant population of the fish have made it to Lake Michigan, it is clear that the electric barriers do not provide fully effective protection for the long term.

Long-term solution

Five states have filed suit in federal court to force the closure of the locks that connect the CAWS to Lake Michigan. Closing the locks, however, would not solve the problem. Even when closed, the locks leak and could allow carp to pass through.

A consensus is emerging that a permanent solution is needed and that it must entail an ecological separation of the Great Lakes and Mississippi River watersheds. This means preventing the inter-basin transfer of aquatic organisms via the CAWS.

A number of governmental agencies and environmental organizations are in the process of studying ways to achieve this separation, including analyzing costs, benefits and impacts. It is likely that an eco-separation will require building a physical barrier (e.g., a concrete wall) to sever the connection between the two watersheds. Depending on the location of the barrier, the impact on recreational navigation could be minimal, and some commercial traffic could still use the waterway. Re-reversing the flow of the Chicago River is also frequently mentioned, although it is too soon to know whether this will be required.