He will try to stay in the middle of the lake because of depthness of water and therefore, more heat. This is the wrong place because he can become trapped if the river freezes. You will need to entice him to stay along the edge near your home if possible. He will be able to use bushes and trees for some shelter. The only other options are to bring him indoors or an animal rehabilitation center for the winter. Are you absolutely sure he cannot fly? The Regal Swan