What the Duck?

This was taken September 11, 2009 at Standley Lake in Westminster, Colorado. At the time, I think I dismissed this as a Mallard. However, as I was reviewing some of my older photos, I realized that there is something wrong with that assessment. The neck and beak appear to be too long.

Now I am thinking this is a Mallard x Northen Pintail hybrid. I would appreciate feedback on this.