Muskrat, Beaver or Groundhog

I spotted this fellow in the Mississippi River not too far from where I live in Minnesota. At first I thought it was a muskrat. But after looking at its head I think it is either a beaver or a groundhog. I think it’s too big to be a muskrat. The nose and eyes I think are closer to a groundhog. I wish I had a better view of his whole body.