More than one hundred years after the reversal of the Chicago River and construction of the Chicago Ship and Sanitary Canal (CSSC), the artificial connections between the Mississippi River Basin and Lake Michigan have come under fire due to the threat of invasive species, namely two species of Hypophthalmichthys carp—colloquially referred to as Asian carp.
You’ve probably heard about the appetite of these fish: carp of one species are known to consume 40% of their body weight every day. Because they eat the same phytoplankton that prey fish in the Great Lakes eat, there’s reason to believe that they could induce a population decline in these fish that feed our game fish species like salmon and trout.
After several years of debate among stakeholders, politicians and industries over the best response to the threat, the emerging consensus solution is that the connection between the Great Lakes and the Mississippi River Basin needs to be removed, permanently. The Great Lakes Commission is preparing to release a study that examines three ways to carry that out:
- The “near-lake” scenario, which places permanent, sediment-based barriers at five different locations in the Chicago Area Waterways System.
- A “mid-system” option, with four barriers located centrally in the CAW
- A “downriver” option, the lowest-cost solution, consisting of a single barrier at the confluence of the CSSC and the Calumet Sag Channel.
The original goal of the CSSC was to improve Chicago’s sewer and stormwater management system. Up until the late 1880’s, it had relied on the river to carry sewage to Lake Michigan, but the stagnant flow made this less than effective. Whenever a heavy rain caused the river level to rise, basements were flooded with a mix of stormwater, river water, and partially-treated sewage. Fears of cholera and typhoid fever transmitted by the contaminated water, as well as concern over frequent flooding persuaded city officials that it was time for a change.
The GLC carefully considered the original goals in their plans, and are confident that the final study will provide both stormwater management and water quality improvements to Chicago residents and prevent the movement of aquatic invasive species. When the study is completed and released in January of next year, GLC expects to recommend one of the solutions for immediate implementation.
Electric barriers are only a temporary solution
Currently there is a system of three electrical barriers on the CSSC designed to disperse approaching fish. According to a March 2011 study release, the U.S. Army Corps of Engineers believes the barrier is working as designed and is effective against fish of varying sizes down to 5.4 inches. According to the results of the study, young carp 1.7-3.2 inches in length might be able to pass through the barriers unharmed.
In February 2010, eDNA testing indicated the presence of Asian carp DNA in Lake Michigan for the first time. Environmental DNA testing refers to detecting genetic material in a water sample, which will contain “shed or sloughed microscopic tissue fragments”, according to the University of Notre Dame’s Center for Aquatic Conservation, where a research group has pioneered the use of eDNA testing in ecological studies. Because each cell in an organism contains a copy of its DNA, all it takes is a few cells; the DNA is then extracted and amplified, and compared to known samples to identify what species those cells came from.
Although the study results are alarming, they need to be taken with a grain of salt. eDNA testing cannot give information on number of fish, age, or gender, or even if the individual fish is living or not. Regardless of these limitations, the eDNA method is still the best and most reliable way scientists have of testing deep bodies of water for the presence of a species.
There’s good news to report, too: it appears that during the last year, the Asian carp front has not advanced. Based on numerous testing methods—electrofishing, netting, eDNA sampling, and others—the estimated location of the population front is still 80-100 miles below the barriers. That’s not to say individual fish haven’t occasionally gotten closer, just that the population has not expanded their habitat up to the barriers.
How much is at stake?
There are still major questions about whether or not Asian carp would establish a viable population if they were to breach the barriers, however. A number of factors would influence their success: plankton densities, winter water temperature, suitable spawning habitat, and many others. Regardless of the expected success of these fish, there is a sizable list compiled by the Great Lakes and Mississippi River Basin Study (GLMRIS) of other species that could become potential invaders. According to GLMRIS, 29 “high-risk” species exist in the Great Lakes that could become invasive if they moved into the Mississippi River via the CSSC, and 10 species besides Asian carp in the Mississippi River Basin that could potentially invade the Great Lakes.
Although there is still plenty of debate, removing the connection between Lake Michigan and the Chicago Area Waterways System would eliminate practically all threat of invasion by Asian carp, as well as other invasive species that could potentially be spread the same way. But what of the potential economic effect on the Chicago area? The closure of the locks would most likely result in a measurable loss to the Chicago economy. However, the Chicago Metropolitan Area GDP in 2008 was $521 billion (Bureau of Economic Analysis, US Department of Commerce); even the most generous calculated loss due to removal of the locks — $1,274,393,287 (Schwieterman 2010)—would amount to only 0.245% of the total GDP.
At this point in the discussion, we also need to consider the consequences of not taking action—which are a lot harder to measure. For example, take that $7 billion-figure people have been throwing around to describe the Great Lakes sport fishing industry. Would every cent of that $7 billion be lost if Asian carp invaded Lake Michigan? Most likely not, but certainly a portion of that amount is at risk. We’d also be gambling on a lot of other assumptions, namely that a species proven to be a successful invasive in the past would, for whatever reason, fail to be so again. Re-reversing the flow of the Chicago River and closing the locks eliminates that risk, and also gives us the opportunity to improve water quality for the City of Chicago and decrease pollution to Lake Michigan–no gambling involved.