- Medium-sized diving duck.
- Rounded head.
- Bill bluish with black tip.
- Male with black head, chest, and rear end, and gray sides (black on the ends and white in the middle).
- Female dull brown, with white patch on face at base of bill.
Male Description Breeding Plumage: Head, neck, upper back, and breast black; head with greenish iridescence. Back white to gray, covered with thin, black wavy lines. Rump black. Belly white. Sides white, with some fine dark streaks. Undertail black.
Nonbreeding Plumage: Similar to female, but with only a few white feathers on face instead of a large white patch. Head and neck blackish brown, lighter on cheeks and chin. Breast dark with some white edging to feathers. Back brown with white edges to feathers. Underparts mottled brownish and white. Tail dark grayish.
Female DescriptionWhite area at base of bill. Head and neck dark brown with some light mottling. Back darkish brown with white flecks. Breast buffy brown. Belly whitish. Sides and flanks brown. Tail dark brown.
Immature DescriptionSimilar to adult female.