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.