Chicago Portage

The Chicago Portage connects the watersheds (BrE: drainage basin) and the navigable waterways of the Mississippi River and the Great Lakes. It crosses the continental divide that separates the Great Lakes and Gulf of St. Lawrence watersheds from the Gulf of Mexico watershed.

The St. Lawrence Seaway Divide runs less than a mile from the shores of Lake Michigan, and is at places only 17 feet (5.2 m) higher than the water level in the lake. A breach of the ridge could potentially cause the Great Lakes to flow southwards to the Gulf of Mexico.

The portage was discovered in 1673 by Europeans when the French Canadian explorers, Louis Joliet and Father Jacques Marquette, were canoeing upstream on the Mississippi River. They received some navigational tips from native Indians and continued along the Illinois and Des Plaines Rivers.

There, according to Joliet, a canal of half a league (about 2 miles (3.2 km), 3 km) across the Chicago Portage would allow easy navigation from Lake Erie to the Gulf of Mexico.

The city of Chicago grew up on the portage.

In 1848 Illinois and Michigan Canal was opened, breaching the water divide and enabling navigation between the two waterways. In 1900 it was replaced by the larger Chicago Sanitary and Ship Canal. After the Chicago River was diverted to the new canal, the Mississippi watershed is now separated from the Great Lakes by only a few downtown Chicago locks. The quantity of water allowed to pass (and thus diverted from the St. Lawrence River) is regulated under international treaty between the USA and Canada.
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