Medium-sized diving duck. White patch in front of eyes. Round white ear spot. Male dark slate-blue with reddish brown sides and odd white patches and spots. Female dusky brown with two or three round white spots on head.
Body plumage slate-blue; white bands and collars, bordered with black lines, on chest and neck; large white crescent in front of eye; small white circular patch near ear; white vertical stripe along side of neck; black streak, bordered by white and amber lines, on top of head; iridescent blue secondaries; rich dark slate-blue belly; chestnut-brown flanks.
Brown body. White belly, with brown checks or spots. Round white spot behind ear. Faded variable white patches in front of eye. Occasionally white streaks on back of head.