In the 1939 case of Wisconsin, Minnesota, Ohio and Pennsylvania v. Illinois and The Sanitary District of Chicago, the states of Wisconsin, Minnesota, Ohio and Pennsylvania filed a lawsuit against Illinois and The Sanitary District of Chicago. They claimed that by diverting water from Lake Michigan into the Mississippi River basin through a canal system for sanitary purposes (to flush sewage away from Lake Michigan), Illinois was lowering lake levels which negatively impacted navigation in other Great Lakes states. This diversion also allegedly violated an earlier Supreme Court decree limiting such diversions to 4,167 cubic feet per second (cfs). However, after considering evidence presented by both sides including engineering reports on water flow rates as well as potential impacts on public health if restrictions were imposed on this sanitation method used by Chicago city officials; the court ruled in favor of defendants - allowing them to continue their current practices without any further limitations or penalties being imposed upon them.

In the dissenting opinion for Wisconsin, Minnesota, Ohio and Pennsylvania v. Illinois and The Sanitary District of Chicago case in 1939, it was argued that the majority's decision to allow Illinois to continue diverting water from Lake Michigan into the Mississippi River basin could potentially cause significant harm to other states around the Great Lakes. The dissenters believed that this diversion would lower lake levels significantly enough to affect navigation and commerce negatively. They also expressed concerns about potential environmental impacts on fish populations due to changes in water flow patterns caused by such a large-scale diversion project. Furthermore, they disagreed with the majority's assertion that there were no viable alternatives available for dealing with Chicago's sewage disposal needs; instead suggesting more environmentally friendly solutions should be explored before resorting to drastic measures like altering natural waterways.