The rich yellow bill with a black saddle on the upper mandible is distinctive. From a distance the plumage appears dark, but less so than that of African black duck. In flight, it shows a blue-green speculum narrowly edged with white.
Juvenile is duller than adult.
Virtually any area of open fresh water, as well as estuaries; often in flocks.
Male gives a rasping hiss, female quacks.