A koi fish just basking. It was so still that the water and reflections were undisturbed and it now looks strange and misplaced in a two dimensional image. The water is a bit murky and that is why the fish is not clear, but the murkiness doesn't effect the reflections.
I liked the explanation; otherwise, I was concerned that and ethereal fish might spontaneously appear in the woods...*chuckle* The reflection is, indeed, clear. That's really cool!