Male. Hejresøen.
Looks odd for a pure Tufted Duck. The pale markings on the bill remind me of a Ring-necked Duck and the shape and color of the head look good for a Greater Scaup. But can't find any similar birds online and don't have access to my duck hybrid literature, why further investigation is pending.
Another rare-looking bird this day. The dark-spotted undertail I don't think matches any pure Aythya, the overall brown colors of the bird look good for a young Greater Scaup as does the head shape and markings, whereas the bill pattern looks better for a pochard. When I first saw the bird sailing in, my impression was that it was light and floating like a wigeon.
Need more material at hand to go further with it, thus, further on id pending.