I was tempted to put this in the article comments forum, but I feel this is more appropriate.
In the SD classics: http://www.straightdope.com/classics/a1_167a.html, which is currently featured, a portion of Illinois, Kaskaskia township, is east of the Mississippi river as a result of a flood in 1881 that redirected the Mississippi.
What’s left of the old river bed?
My guess is that it is one big bow lake. It may be safe to assume that some boats and barges got caught in this lake. Are any preserved and on display? Who has been there? What’s it like?
You can see the Mississippi river on the right, and from the south side comes around a little river extension. Also you can see the few buildings that make up the town of Kaskaskia pretty much in the center of the picture. On the other side of the river is the town of Chester.
I have my Delorme Illinois Atlas and Gazetteer open on my lap here. The Illinois state boundary as indicated on this map–that sort of bulging loop out to the west and back again to the Mississippi–is indicated on the Gazetteer as a yellow highlighted “Illinois State Line” that’s exactly following the bed of a thin blue line marked “Old River” on the south, and “Idlewild Slough” on the north. The thin blue line is what Delorme uses to indicate a small waterway, like a stream, ditch, or canal. The Mississippi River itself is an imposing quarter-inch width of “blue”, and even its other oxbows are large blobs of blue. But this particular oxbow is nothing more than a tiny stream, and it’s slowly filling in–that’s what a “slough” is.
You can see the filling-in oxbow quite clearly on the Terraserver picture.
Look at the bright white loop that goes up and around on the west side of the picture, enclosing the light-colored croplands. That’s a road, and on the Delorme it’s paralleling a second thin blue line to the east of the first one. Now, paralleling the road, about a finger’s width all around it on the outside (the “Missouri” side), except for the north, there’s a band of much darker stuff. The outside perimeter of that band of darker stuff is what’s marked as the Illinois state line on the Delorme. That’s the old riverbed–that band of darker stuff, now slowly filling in to make a slough instead of flowing water. The “canal” that the road is paralleling used to be part of the Mississippi River.
Look in the southwest corner. There’s a sort of T-intersection. That’s a road leading up to the bluffs and the town of St. Mary. See how the band of darker stuff indicates that the river once flowed right up under the bluffs.
The southern and eastern parts of the filled-in oxbow are so much darker than the northwestern part because, according to the gazetteer, they’re wooded.