The Pacific Black Duck has a mottled dark brown body. The head is dark brown with a cream stripe above and below the eye, dark stripe through the eye. The white underwing is distinctive in flight. The introduced Mallard may interbreed with the Pacific Black Duck and the offspring are a brownish colour, with a partial eye-stripe and orange legs.
The Pacific Black Duck is a common breeding resident of freshwater lakes and rivers or sheltered coastal waters. They are usually seen in pairs or small flocks, readily mixing with other ducks. They are mainly vegetarian, feeding on the seeds of aquatic plants. They supplement the diet with small crustaceans, molluscs and insects.