This large duck with its grey-speckled head and contrasting blue-black and white plumage is unmistakable. In flight the wings are black and unmarked; female shows a little white on the lower back.
Male is larger than female and has a rounded protuberance on the bill that enlarges conspicuously during the breeding season. Female lacks the bill development of breeding male and is smaller. Juvenile and immature resemble female but are duller, and have dark speckling on the breast, belly and flanks.
Mainly on pans and dams in woodland and along large rivers in the north. Nests in a large hole in a tree.
Whistles, but usually silent.