The canal was primarily built as a sewage treatment scheme. Prior to its opening in 1900, sewage from the city of Chicago was dumped into the Chicago River and flowed into Lake Michigan. The city's drinking water supply was located offshore, and there were fears that the sewage could reach the intake and cause serious disease outbreaks. Since the sewer systems were already flowing into the river, the decision was made to dam the river and reverse its flow, thereby sending all the sewage inland where it could be treated before emptying it into the Des Plaines.