The male, or drake, is very recognisable nearly all year round by its metallic green head, brown breast that is delineated from the head by a white neck ring, grey body and black tail. During the summer months, June to September, the drake moults and looks very similar to the female - this is called "eclipse" plumage - and offers better camouflage until their flight feathers have been fully replaced. The female, or duck, is mainly brown, with blackish mottling and has a plain buff coloured head with a dark line through the eye. Both sexes have a purple-blue speculum. Further, they both have orange-red legs and a yellow-olive coloured bill, but the duck's bill is much duller.

Mallards are dabbling ducks, so they forage near the water surface or upend to reach food deeper down, but also feed off the ground. The diet comprises cereals, plants and invertebrates, and less often fish. They will visit gardens for these foods.

The Mallards build a nest, from leaves and grasses, among dense vegetation. Mallards may be hunted September to January, but are protected during the breeding season. Despite this, the non-breeding population has declined moderately over the last 25 years.