The Chatham duck or Chatham Island duck (Pachyanas chathamica) is an extinct species of duck, in the monotypic genus Pachyanas, which once lived in New Zealand’s Chatham Islands in the south-west Pacific Ocean. It was described by Walter Oliver (as a "stoutly built duck") from bird bones in the collection of the Canterbury Museum in 1955 in the second edition of his work New Zealand Birds.