Petra Thümer (later Deckert then Katzur, born 29 January 1961) is a former swimmer from East Germany. She won gold medals in the 400 m and 800 m freestyle at the 1976 Summer Olympics and the 1977 European Aquatics Championships. During her career she set five world records in the 400 m and 800 m freestyle. In 1987 she was inducted into the International Swimming Hall of Fame.