The reversal of the Chicago River was a pioneering, massive public works effort that saved the Chicago region from waterborne diseases caused by sewage contamination of its drinking water supply - Lake Michigan. The City's sewers discharged human and industrial wastes directly to its rivers, which in turn flowed into the lake. A particularly heavy rainstorm in 1885 caused sewage to be flushed into the lake beyond the clean water intakes. The resulting typhoid, cholera, and dysentery epidemics killed an estimated 12 percent of Chicago's 750,000 residents, and raised a public outcry to find a permanent solution to the city's water supply and sewage disposal crisis. In 1889, the State of Illinois enacted a law enabling creation of the Sanitary District of Chicago (which continues to exist today as the Metropolitan Water Reclamation District of Greater Chicago) for safeguarding Chicago's water supply. It would do so by constructing canals to make the Chicago River flow backwards, away from the lake. The system of three canals was built from 1892 to 1922, first with the pioneering 28-mile long, 24-foot deep, and 160-foot wide Sanitary and Ship Canal (begun in 1892 and completed and placed in operation in 1900), and later with the North Shore Channel (1910) and the Cal-Sag Channel (1922). The Sanitary and Ship Canal was cut deep through a low point on the continental divide located a few miles west of Chicago which separated the north and east flowing Chicago River from the south and west flowing Des Plaines River. This canal reversed the flow in the Chicago River toward the Mississippi River and Gulf of Mexico, diverting sewage away from the Lake Michigan water supply. Water pulled from the lake flushed Chicago's riverborne sewage and provided dilution and aeration, which was a conventional sanitary engineering methodology at the time. As Chicago resumed its rapid growth with the canals in place, their self-cleansing ability was quickly outstripped by the sewage loading. This led to the District implementing large scale, modern (activated sludge) sewage treatment plants, beginning with the Calumet Treatment Works (1922), and including the Stickney Sewage Treatment Works southwest of Chicago, the world's largest at 1.2 BGD (1931). Although environmental health was the main purpose of the river reversal project, the canals were also designed and intended to boost Chicago's and the Midwest region's economic development by providing the critical link for eventual intracontinental water shipping transport from the North Atlantic at Canada's St. Lawrence River, to the Gulf of Mexico by way of the Great Lakes, Chicago River/Canal, and the Des Plaines, Illinois and Mississippi Rivers. The Sanitary and Ship Canal was constructed at an estimated cost of over $70,000,000. After its completion, waterborne disease rates quickly and dramatically improved, and its water supply system was soon regarded as being one of the safest in the world. With its water source made safe and dependable by the canals, Chicago and the region grew and prospered rapidly. The reversal of the Chicago River was the largest municipal earth-moving project ever completed, and was hailed as a monumental engineering achievement. Significant new excavation technology and techniques developed and perfected on the project contributed to the construction of the Panama Canal. In the 21st Century, the canals continue to serve crucial pollution control, flood control, and navigational needs.