Historic Hydrology

Chicago's hydrologic history is one of the primary reasons that early settlers established Chicago here. This geographic location is the shortest distance of land between the two largest water navigation routes of the continent, connected via the Great Lakes-St. Lawrence seaway reaching the Atlantic Ocean to the east and the Mississippi River watershed to the west and south reaching the Gulf of Mexico. 

Chicago's hydro-geographic advantages however also proved to be its biggest challenge.


The City of Chicago and Cook County lie within the Great Lakes Physiographic Province, a glaciated landscape, across which sands, gravels, and till soils were deposited by the advancing and retreating glaciers. The deposited soils were then distributed by winds and by water through rivers and lake currents. The eastern half of Cook County (area in blue-gray), including the City of Chicago, lies in within the Chicago Lake Plain section, composed of a low flat topography, consisting of glacial till, with sands & gravels along the coastal zone and waterways. The western half of Cook County (area in orange) sits along the Wheaton Valparaiso Terminal Moraine subsection, which forms the topographic watershed divide (the high-ridge) between the Great Lakes and the Mississippi River watersheds.

After the final glacial retreat about 14-15,000 years ago, Lake Chicago was covered by water until about 10,000 years ago when it drained through a low point in the terminal moraine to the west. A wet marshy landscape remained, lined by dunes and sandy gravelly spits along the coastal areas. Prairie streams (upper image) meandered across the plain, draining the low-plain landscape to the Great Lake to the east. However, the western end of one of the prairie rivers (today called the Chicago River) flooded seasonally providing a floatable connection across the landscape. This flooded area was called the Chicago Portage; it linked the shortest geographical distance between the Great Lakes and St. Lawrence Seaway to the east, and the Mississippi River system to the west, creating a navigable connection across a major part of the continent. 


This geographical location was strategic for navigation and trade. However, Chicago's natural history proved challenging for urbanization of Chicago. The urban ground was very flat and seasonally wet. 

Over time, the City struggled with the wet nature of the landscape, raising buildings and streets, and piping waste water and rainwater away into rivers. Without proper sanitation methods, its wastewater was reaching its drinking water source Lake Michigan. Through a series of hydraulic projects in the mid to late 1800's, the City decided to reverse the flow of the Chicago river that carried its waste. By digging a canal to the west, it reversed the flow of the Chicago river and therefore its waste westward, hydraulically engineering its way out of its natural watershed. Today the City maintains this westward flow through a combined sanitary-sewer system.

Thus, the landscape which historically contained a complex variety of natural hydrologic features such as lakes, streams, marshes, wetlands, and coastal dunes was increasingly drained, flattened, and conveyed into a westward flow as lines in the landscape.

This map depicts the location of the canals and remaining lakes (in dark gray). These water bodies are familiar to 21st century Chicagoans. Also presented, depicted (in blue) are the historic footprints of lakes,  wetlands, and shorelines that have been altered and disappeared through draining, piping, and canalization. 

Of particular interest is the modification to Chicago's primary inland waterway, the Chicago River. While the top image gives an excellent idea of what the prairie river looked like prior to canalization, the lower image is of the Chicago River through the downtown Loop today.