Small individuals of this species are the smallest waterfowl on earth, at as little as 160 g (5.6 oz) and 26 cm (10 in). White predominates in this bird's plumage. Bill short, deep at base, and goose-like.
Male in breeding plumage is glossy blackish green crown, with white head, neck, and underparts; a prominent black collar and white wing-bar. Rounded head and short legs. In flight, the wings are green with a white band, making the male conspicuous even amongst the huge flying flocks of the Lesser Whistling Duck, which share the habitat. Female paler, without either black collar and only a narrow or nonexistent strip of white wing-bar. In non-breeding plumage (eclipse) male resembles female except for his white wing-bar. Flocks on water bodies (jheels), etc.