The Arkansas river joins the Mississippi between Rosedale, Mississippi and Arkansas City, Arkansas. From the right side, of course - the west.
It's the most notable confluence since the Missouri all the way up above St. Louis, in terms of the way the waters mix. The Arkansas comes in clear and dark and green - so green it's almost, but not quite, the Chicago River St. Patrick's Day green. This green is darker, deeper, more natural. I tested the turbidity, just for giggles, and sure enough: 45.5cm! For reference, the Mississippi has lately been down around 18cm.
The Mississippi is now fully inhabiting its Big Muddy reputation. It's very turbid, not just brown but sort of a light chalky brown. Sometimes with some pretty nasty-looking stuff in it. And not just bits of wood, but whole trees floating down the stream. Seeing this much clearer water join in is pretty fun - a reminder in reverse of the old days, when the Mississippi was the clear one, accepting a load of silt from the Crow, the Minnesota, the Illinois.
I filled both water bottles with filtered Arkansas water, just because it looked so much more pleasant to drink. And I was right - it was very nice.