Size: L: 50cm (male tail feathers 15cm). Wt: Males: 850 g. Females: 760 g. Sexually dimorphic in colour, and also slightly in size. This species is not seasonally dimorphic.

Male: upperparts grey, with elongated, white-edged feathers, and dark brown speculum; sides grey; head brown, with darker crown and nape; neck white, with white extending in thin line onto head; underparts white; tail black, with elongated central rectrices; bill black, with broad, blue lateral stripes

Female: upperparts mottled brown, with dark brown speculum edged in white; head paler brown, with whitish chin; breast and flanks mottled brown; belly white; tail mottled brown, long and wedge-shaped, but lacking elongated feathers of male; bill as in male

Duckling upperparts brown-black, with several white stripes on back; double line through eye, lower stripe incomplete; underparts, edge of wing, and face buffy white; some orange-brown markings on face.