Accordging to my map, the Platte River joins the Mississippi in the massive pool above Dam #11. The confluence looks major, on paper. It was on the left bank, and I was on the right. I was hard pressed to figure out where it even was.
I know that I'm missing a lot of confluences in this section of river. The Zumbro and others have joined the Mississippi in ways that I could not see, did not recognize. It's interesting, because in the early days on the river any significant addition was a major event. Now even a significant river debauching into the Mississippi can occur without notice.