Size: L: 40 cm. Wt: 500-600g. Sexually dimorphic in colour, but only slightly in size. This species is seasonally dimorphic.
Breeding Male: crown and nape black; large white cheek patch; throat and body dark chestnut; belly white; bill blue; tail dark, often held in erect position.
Breeding Female: crown and nape dark brown; face whitish, with dark horizontal stripe; back dark brown; underparts pale mottled brown; tail dark, not held erect; bill dark grey.
Winter Male: similar to breeding female, but white face with no stripe.
Winter Female: similar to breeding female, but paler overall.
Duckling: downy; dark grey-brown above; white below; white stripe from bill to nape; pale spots on back.