In the late 19th century, Chicago faced a serious public health crisis. The city's drinking water came from Lake Michigan, but the Chicago River, which flowed into the lake, was also used to carry sewage. This led to the contamination of the lake, resulting in outbreaks of diseases like typhoid, cholera, and dysentery. A major storm in 1885 worsened the situation, causing widespread illness and deaths. This crisis led to the formation of the Sanitary District of Chicago in 1889, whose main goal was to prevent sewage from entering Lake Michigan by reversing the flow of the Chicago River. To achieve this, engineers constructed the Chicago Sanitary and Ship Canal, a massive 28-mile waterway completed in 1900. The project involved moving large amounts of earth and rock using steam-powered equipment and dynamite. The chief engineer, Isham Randolph, later used the techniques he developed for this project when working on the Panama Canal. The reversal of the river's flow had immediate health benefits, with studies showing a 4% drop in overall mortality rates by 1900, which saved nearly 1,000 lives. The canal was later recognized as one of the "Seven Wonders of American Engineering" by the American Society of Civil Engineers in 1955. However, the canal also had unintended environmental consequences. It created a permanent link between the Great Lakes and the Mississippi River basin, which had previously been separated by a natural water divide. This connection allowed invasive species like zebra mussels and round gobies to spread between the two regions. Researchers have identified several high-risk points in the canal where invasive Asian carp could potentially move, threatening the ecosystems of the Great Lakes. To address the invasive species problem, the U.S. Army Corps of Engineers installed an electric barrier in the canal in 2002. While some consider this a temporary measure, others believe it is an effective solution. A more permanent plan to separate the basins has been estimated to cost over $1 billion. Additionally, the canal has been linked to environmental changes, including a drop in Great Lakes water levels in the 1990s. Although some experts have suggested reversing the river's flow again to restore the natural boundary, this idea has not been implemented. What began as a public health solution has since become a complex environmental and engineering challenge.