Eons ago, when the ice age was in its decline and the glaciers that covered the earth were receding, there was a very large glacial lake known as Lake Chicago that covered the area that is now Riverside. As the glaciers receded, they cut a path through this vicinity that ultimately left a chain of great lakes and a ridge or continental divide that surrounded one of those lakes--Lake Chicago that covered the area that includes Riverside, that ridge narrowed and divided the waters of the Chicago and DesPlaines rivers. During high water periods, the Des Plaines emptied part of its water into Lake Michigan through the south branch of the Chicago River and during low-water periods, the shallow channel or slough that formed was known as Mud Lake.