Researchers with the U.S. Geological Survey discovered that the Chicago watershed delivers the most nitrogen and phosphorus to the Mississippi and hence to the Gulf of Mexico, where it fertilizes algae blooms that suck up the oxygen and creates a Dead Zone.
“We could go with ease to Florida in a bark and by very easy navigation. it would be necessary to make a canl, but cutting through a half league of prairie, to pass from the foot of Lake Michigan to the Des Plaines River.” –Louis Joliet, 1673
What would be an easy route for navigation would also be an easy route for sewage, nitrogen, and phosphorus. The only impediment to navigation and sewage was the Chicago Portage, a low continental divide just west of Chicago.
Native Americans recognized that the Chicago Portage was the shortest route between the St. Lawrence River, which drains to the Atlantic, and the Mississippi, which drains to the Gulf of Mexico.
Pere Jacques Marquette and Louis Joliet returned to Lake Michigan after their discovery of the Mississippi, a trip which took them as far south as the Arkansas before they turned back. They began their trip in Green Bay, which took them to the Fox River, across a divide to the Wisconsin, and down the Wisconsin to the Mississippi.
They returned to Lake Michigan via the Illinois River, the Des Plaines River, and the Chicago Portage.
The Des Plaines is the northern branch of the Illinois and flowes from southern Wisconsin south parallel to and five miles west of the Illinois shore of Lake Michigan. The river turns south west two or three miles east of a swamp known as Mud Lake, which fed both the Des Paines and the south branch of the Chicago River, which flowed into Lake Michigan at the future site of Chicago.
Native Americans and pioneers in canoes could portage from one river to the other across Mud Lake, but travelers in larger boats could not. When Marquette and Joliet crossed the swamp in 1673, Joliet noted that a canal could connect the two rivers and make passage to the Mississippi from Lake Michigan easy. Several, years later LaSalle, who traveled down the Mississippi to the Gulf, noted that the upper reaches of the Illinois River were unnavigable to Peru, Illinois and any canal that connected the Illinois to Lake Michigan would have to bypass that section of the Illinois.
In 1848 the Illinois and Michigan Canal did just that.
The canal that connected the Great Lakes to the Mississippi cut a channel through solid rock from the south branch of the Chicago River to the Chicago Portage, which separated water which flowed to the Atlantic from that which flowed to the Gulf of Mexico. It crossed Mud Lake and ran parallel to the Des Plaines and Illinois Rivers.
A Lock and Dam at Lockport, sluice gates at Chicago Harbor, a Lock and Dam on the Calumet River, pumps at Wilmette harbor control the flow of water through the system.
In 1900 the Chicago Sanitary and Ship Canal, 28 miles long, replaced the Illinois and Michigan Canal and connected Lake Michigan to the Des Plaines River. Before its construction, Chicago dumped its sewage into Lake Michigan, from which the city also drew its drinking water.
In essence, engineers reversed the flow of the Chicago River, made a second cut through the divide, and sent Chicago’s sewage to the Mississippi. In 1907 it was extended to Joliet. In 1910 a second canal, the North Shore Channel, was added to the system, and a third, the Cal-Sag Channel was added in 1922.
I have this fantasy that should any or all of the dams failed, the Great Lakes would drain to the Gulf of Mexico.
And that’s how Chicago’s sewage, today treated sewage, and nitrogen and phosphorus, gets to the Gulf of Mexico and contributes to the Dead Zone.