Photographer James Kusz spotted and photographed this extraordinary Mallard. It’s a white-breasted brown Mallard. Mallards are known for hybridizing with other waterfowl, with or without consent, and sometimes the result looks like this. Very likely the other parent was a white domestic duck, probably also a Mallard descendant. Photos of this and similar hybrids are collected on this website.
It’s hard to tell whether this is a male or a female. The body coloring suggests female but the green head points male. I guess we just have to wait and see.