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[1] and the 1977 European Aquatics Championships.

[2] Later she admitted to using performance-enhancing drugs as part of the East German training system.

[3][4] For this reason she missed the 1978 World Championships – coaches feared she would not pass the doping test and excluded her from the East German team, officially explaining her absence by injuries.

[3] She was married to the German Olympic athletes Klaus Katzur (swimmer) and Alf-Gerd Deckert (cross-country skier).