- Medium-sized diving duck.
- Chunky body.
- Large head.
- Male white with black back and head, and crescent-shaped white spot on face.
Breeding (Alternate) Plumage: Head purplish-black. Bright crescent-shaped white patch on side of face at base of bill, thin at top, rounded at bottom. Sides, breast, belly, and secondaries bright white. Back, wings, and tail black. Black of back reaching onto shoulder. Series of white squares along sides above wings. Short, triangular black bill. Eyes golden yellow.
Nonbreeding (Basic) Plumage: like female, but with some black tinge at sides.
Female DescriptionHead chocolate brown. Back, wings, and tail slaty gray. Flanks, belly, and breast white. Eyes pale yellow to white. Short, triangular bill mostly yellow.
Immature DescriptionImmature similar to female. First winter male similar to adult male, but has browner head, gray sides and chest, and smaller and less distinct white crescent on face.