By 1887, it was decided to reverse the flow of the Chicago River through civil engineering. Engineer Isham Randolph noted that a ridge about 12 miles from the lakeshore divided the Mississippi River drainage system from the Great Lakes drainage system. This low divide had been known since pre-Columbian time by the Native Americans, who used it as the Chicago Portage to cross from the Chicago River drainage to the Des Plaines River basin drainage. The Illinois and Michigan Canal was cut across that divide in the 1840s. In an attempt to better drain sewage and pollution in the Chicago River, the flow of the river had already been reversed in 1871 when the Illinois and Michigan Canal was deepened enough to reverse the river's flow for one season. A plan soon emerged to cut through that ridge and carry wastewater away from the lake, through the Des Plaines and Illinois rivers, to the Mississippi River and the Gulf of Mexico. In 1889, the Illinois General Assembly created the Sanitary District of Chicago (SDC) to carry out the plan. After four years of turmoil during construction, Isham Randolph was appointed Chief Engineer for the newly formed Sanitary District of Chicago and resolved many issues circulating around the project. While the canal was being built, permanent reversal of the Chicago River was attained in 1892, when the Army Corps of Engineers further deepened the Illinois and Michigan Canal.