- Medium-sized diving duck.
- Slight bump or peak on back of head.
- Bill bluish with small black tip.
- Male with black head, chest, and rear end, and gray sides (black on the ends and white in the middle).
Male Description Breeding (Alternate) Plumage: Head, neck, upper back, and breast black; head with purplish iridescence. Back white, covered with thin, black wavy lines. Rump black. Belly white. Sides white, with some fine dark streaks. Undertail black.
Nonbreeding (Basic) Plumage: Similar to female, but with only a few white feathers on face instead of a large white patch. Head and neck blackish brown. 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.