The Cal-Sag channel, a shortened name for "Calumet-Saganashkee Channel," was dug in 1922 by the Metropolitan Sewage District of Chicago. It runs just above the northern perimeter of Lake Katherine. The sixteen-mile channel connects to the Little Calumet River on its eastern end, runs west past the Saganashkee Slough, and connects up again on the west with the Chicago Sanitary and Ship Canal.
The channel was dug for the purpose of changing the flow of the Calumet rivers to help divert some of the sewage and waste away from Lake Michigan toward the Illinois River.
Developments near Lake Katherine needed to get rid of excess storm water so the lake was turned into a mechanism that aerates and filters the water using waterfalls and other natural processes before it passes over a spillway into the Cal-Sag Channel.
Along one of the winding paths through the Eastern Preserve at Lake Katherine is an attractive overlook with benches that provides visitors a beautiful view of the Harry 'Bus' Yourell Off-Stream Aeration Pool, which is a lovely sight and includes scenic bridges and wooded areas as well as several waterfalls which tumble into the Cal-Sag channel.