Conventional sewage treatment helps achieve that goal by skimming human and industrial waste, treating it with microbes to break down organic matter and disinfecting what's left before releasing it into lakes or streams. Federal and state regulators allowed the district to skip the last step for decades because few thought anyone would want to come near putrid waterways that were reversed at the beginning of the last century to flow away from Lake Michigan, an engineering feat that separated the region's waste from its source of drinking water.