This one's a head scratcher. The colorful bill, white on the cheek and the way he's holding his tail make me think of a wood duck(and the size was close, 70-80% the size of the mallards in the area). Would probably be a pretty bird with feathers in better condition. Found it in a park in my area(NC Iowa) where people spend a lot of time feeding the ducks, and released domestics aren't uncommon.
Edit-got a reply though another forum that it's a feral Muscovy.