Nice low angle and specimen. Good job on a tricky exposure. I think a touch more contrast might look good here, and I would lose the blue patch in the upper left corner
Dependant on your use for this image, I might be tempted to clone out the bright patch in the water top left as we look at the picture. That just draws my eye a little.
A beauty, Jonathan! To improve this, I believe a little CW rotation is in order. He seems to be swimming up hill? If you look at the eye and the eye's reflection, I believe the line between should be parallel to the frame edge. Great capture!
+1 on all the above comments: great detail, exposure, and perspective. Looks very much like our American scaup (except for the tuff!).
I would be tempted to crop tighter on top. Nothing particularly attractive up there - it would eliminate the blue blotch and move the bird higher in the frame.