The webbed feet, used for propulsion in both swimming and diving, are 5–7 cm long, large for the size of the birds, and dark grey to blackish in all the species.

[7][8] The species occur throughout Asia, Europe, North America, Australia, New Zealand, and Madagascar, and also in the northern half of Africa primarily in winter.

[8][10] The diet, mostly obtained by diving to depths of 0.5–6 m (exceptionally 10 m), but also at times from the surface without diving, consists of a mixture of plant material (including seeds, leaves and roots of water plants) and bottom-dwelling invertebrates (including worms, molluscs, insects).

In urban situations, several species have learnt to take bread or birdseed fed to ducks by people.

[7][11] The nests are hidden in dense waterside vegetation, for preference on islets which give greater security from land predators.

Zelenkov (2016) transferred the species Anas denesi Kessler (2013), known from the late Miocene of Hungary, to the genus Aythya.