In 1892, engineers began the Chicago Canal to divert sewage using 42 million cubic yards of earth; more than a century later, it may help Asian carp reach the Great Lakes

In 1885, Chicago drew its drinking water from Lake Michigan, the same lake the city used as a dumping ground for untreated sewage. Cholera and typhoid were wreaking havoc among the population. The solution adopted by the city was not that of building better sewage systems but to reverse the flow of a river to dump the waste into it.

As reported by Kenneth Olson and Lois Wright Morton in their 2017 paper titled “Chicago's 132-year effort to provide safe drinking water,” published in the Journal of Soil and Water Conservation, this effort to protect the water supply of Chicago that dates back more than a century and is centered on the Chicago Sanitary and Ship Canal has entailed repeated intervention through engineering, such as the reversal of the Chicago River, creation of canals, as well as construction of offshore water intakes, amid pollution and contamination issues brought about by fast urbanization. This is a distinct saga: address the problems of today with a huge, expensive, and somewhat risky infrastructure project, then deal with its consequences for the next hundred years.

Digging more dirt than the Panama Canal


Construction work for the Chicago Canal began in 1892 and ended in January 1900. About 42 million cubic yards of soil were excavated, an amount sufficient to fill today’s Willis Tower twenty times, with steam shovels and manual labor. At that time, “heavy machinery” was a relatively new concept. Historically, this has been considered to be the largest earth-moving effort undertaken until then in North America.

The methods used here were later used by engineers to construct the Panama Canal. As a result, the sewage that was flowing into Lake Michigan started flowing south, into the Mississippi Basin, away from the drinking water of Chicago. Missouri, representing St. Louis's interests downstream, sued Illinois and the Sanitary District of Chicago over the diversion, taking the case to the U.S. Supreme Court in Missouri v. Illinois (1901 and again in 1906); the Court ultimately declined to block the discharge.

The unintended side door for an invasive fish

However, the very same canal that shields Lake Michigan from sewage contamination is the shortest wet route from the Mississippi River Basin into the Great Lakes. The problem of Asian carp is severe in the Mississippi Basin: these carp species, namely, bighead and silver carp, were accidentally released from fish farms and gained dominance within sections of the river system. Individual carp and their environmental DNA have already been detected on the Lake Michigan side of the barriers meant to stop them, though biologists say a breeding population has not yet become established in the Great Lakes. If that changes, they warn, the connected lake system could be at risk. The Great Lakes fishery, commercial and recreational combined, across the U.S. and Canada, has been estimated at roughly $7 billion annually by the Great Lakes Fishery Commission, though more recent, narrower estimates of the U.S. recreational fishery alone put the figure closer to $5 billion.

Enter the underwater electric fence

The US Army Corps of Engineers’ solution involves the use of sets of electric dispersal barriers that have been installed at the canal near Romeoville, Illinois, and deliver current into the water, forcing the fish to reverse their movement before reaching the lake.It's an unusual, almost dystopian fix, and a temporary one. At least, the US Army Corps of Engineers’ Great Lakes and Mississippi River Interbasin Study (GLMRIS) report presented to Congress in 2014 suggests eight possible alternatives for long-term solutions, with one of them being a complete physical separation of the two basins.

The GLMRIS report itself priced separation options at $15 billion and up; an earlier, separate 2012 study by the Great Lakes Commission and the Great Lakes and St. Lawrence Cities Initiative had estimated a less extensive mid-system separation could cost between $3.2 and $9.5 billion, a discrepancy that became a point of contention once GLMRIS came out with higher figures. None of the separation plans simply wall off the basins and stop there: they pair any barrier with new infrastructure: sewage tunnels, pumping stations, and water-treatment upgrades, meant to keep routing Chicago's wastewater away from the lake even after the canal itself is closed to fish and boats. Without that added infrastructure, closing the canal would undo the very protection the 1900 reversal was built to provide.

The skeptical part

The construction of a canal in order to resolve one environmental issue led indirectly to creating another issue. And over a century later, the United States continues to repair that problem through the use of electricity rather than resolving the fundamental problem of two separate river systems that were not supposed to be connected via a water and sanitation passage in the first place, which Chicago cannot close down now without disrupting commerce in the region. Even a historic public health victory has its feet planted on the ground.

A 2025 study titled “The Chicago River Reversal of 1900: Separating Myth from Measured Impact on Public Health,” published in medRxiv, analyzes the death rate statistics and suggests that while there was a positive impact on mortality rates, it was rather insignificant in terms of numbers: around a 4% reduction from the pre-existing rates rather than an instant improvement that some textbooks might offer. As a preprint, that paper has yet to undergo peer review, but it's worth noting that legendary engineering solutions are rarely as foolproof as the legend makes them out to be. The Chicago canal remains both a success and cautionary tale: a century-old fix for one crisis that opened a new front, the fight against Asian carp, which engineers are still managing one electrified stretch of water at a time.