This is a massausagua rattlesnake, can be found along the Mississippi and tributaries and range from Southern Ontario southward thru the midwestern states. I’ve had an encounter or two with them on sandbars near Wabasha. They will swim and have no aversion to doing so. They tend to be nervous little snakes and seldom get more than a couple feet in length.
Notice the color similarities between the rattlesnake and the pictured snake above. If you look closely at the one in the original post you may note the triangular head, typical of rattlesnakes while a bull snake will have a rounder head I think. The thing with the Massausagua is that it has less well developed rattles, if any other than a hard nub or two.
The top picture could easily be one of these rattlesnakes. Do a BING search on the rattlesnake and you’ll be gifted with a bazillion different color variations of the rattler. This picture was taken from the BING site.
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