I had to do some research when I got home to make sure I knew what this was. I saw the head in the water as it swam around but it was at a similar time to when I saw a mink. Consequently, I wasn’t sure what I was looking at when. A little use of Google later and I was able to confirm that this was indeed a muskrat. They look very small when swimming since they are almost completely submerged. Once out of the water, they look a lot more substantial, and that tail is very distinctive.
He climbed out on to a branch that was floating in the water. It looked like someone else had previously been on the branch judging by the droppings that were there, and these didn’t seem to bother him much. Maybe they were his from a previous visit. A quick trip along the branch and back and then it was back into the water. Another time I saw one, the same routine of walking along the branch and back was repeated so maybe it was the same one?