Male and female have different coloured neck and heads. Males have a green neck, the face is white edged dark green below the eye and there is a a white patch on the face below the eye, chin is grey, top of the head is dark green/brown. Females have a narrow, vertical band down the back of the neck but the rest of the neck is white, slightly flecked with green. The side of the face is white. Female head is less green than the male and there is a white eyebrow. Non-breeding adult males have brown blotches on the facial white patches.
Immature birds resemble females but the face, chin and neck are heavily spotted with dark brown; by the time they are two months old males begin to grow solid green necks. Unsuccessful breeding males may go into eclipse with white flecks on the face, chin and neck.
The Green Pygmy Goose is one of the most water-loving ducks and is usually found in small groups in tropical freshwater lagoons. Mostly aquatic, feeding and resting on water, rarely on a perch or on land; they walk with difficulty and are awkward on land, although they sometimes leave the water and rest on partly submerged fallen trees. This bird is reluctant to fly but when it does so it springs from the water at a low angle and flies fast and low, in a direct line, whistling as it goes. The Green Pygmy Goose swims and dives strongly
Feeds almost exclusively on aquatic vegetation cruising among water lilies grazing on buds and emerging plants. Dives to half a metre deep to reach submerged plants. Also filters floating seeds and flowers from the water surface.
The Green Pygmy Goose is sedentary and usually seen in pairs. In the dry season it forms flocks of several hundred birds on the most permanent lagoons, particularly deep, permanent freshwater dams and lagoons. In the wet season birds spread across coastal plains to breed in the deepest swamps and ponds.
Nesting takes place in January to March near Darwin and in northern Queensland. Nests are made in swampy vegetation, on the ground, or in hollows of trees standing in water. The male finds several possible nest sites but the female makes the selection. There are eight to 12 eggs, hard-shelled, smooth and lustrous, cream or white, blunt ovals, about 44 by 32 millimetres. Incubation takes 26 days, the female broods the eggs. The male defends the nest area while the female is brooding and help rear the young after the eggs hatch. Chicks can dive to escape danger and freeze under water lilies until the parents return.
Found along a broad coastal strip from Broome along the north coast to the Queensland coast south of Rockhampton. Locally common and sedentary or nomadic.