I don't know how to describe it but this picture just feels so *right*. The tone, the colours, the shiny-ness of the water on the swans chest, the way the red eye catches the light... it's just really great.
What really caught my eye was the color of the muddy water, in many ways it enhances the shot. It gives the appearance of a sepia tone, the swan's black feathers seem to pick up more brow/ yellow in them and it tones down the red of the beak. I actually think this shot would not be as interesting it the swan was on clear water. Great job, the moment is perfect!