So reading about the the Chicago Sanitary and Shipping Canal, you can see on the map that the route travels about 15 miles parallel to the Des Plaines River.

I've been trying to find out why. This was built in the old days, very hard and expensive labor even with primitive steam shovels, and very expensive. But I cannot figure out why they went this extra 15 miles when they could have just cut the path straight into the Des Plaines.
I did find the older Illinois and Michigan Canal and for some reason this one too took a southern turn instead of continuing west into the Des Plaines, which would be a much shorter route.
Was there something wrong with the Upper Des Plaines that made it unavigable to shipping? Was there some expensive land or buildings that they didn't want to encroach upon? Every cause that I can think of, when searched specifically, gave me no good results. So I'm now more curious than ever. There must be a reason for this longer route in both canals.