It measures 58–72 cm (23–28 in) in length, with a wingspan of 78–97 cm (31–38 in), and weighs between 0.9 and 2.1 kg (2.0–4.6 lb). Males are generally slightly larger than females, though there is some overlap in size. Like other species in the Mergus genus, it has a crest of longer head feathers that usually lie smoothly rounded behind the head, rather than forming an erect crest. Adult males in breeding plumage are easily recognizable, with a white body that has a variable salmon-pink tinge, a black head with an iridescent green sheen, a grey rump and tail, and wings that are white on the inner half and black on the outer half. Females and males in “eclipse” (non-breeding plumage from July to October) are mostly grey, with a reddish-brown head, white chin, and white secondary wing feathers. Juveniles of both sexes resemble adult females but also have a short black-edged white stripe between the eye and bill. The bill and legs are red to brownish-red, with adult males having the brightest coloration and juveniles the dullest.