Dutch competitive swimmer Jopie Waalberg represented Amsterdamse Dames Zwemclub where she specialised in the breaststroke. Waalberg swam at the 1936 Berlin Olympics and a year later she became the first woman to swim the 200 metres breaststroke in under three minutes. At the Berlin Games she swam in her favoured event where she finished joint-fourth in the final with Hanni Hölzner. The following May she set a world record in the same distance with a time of 3:00.2, before setting the first sub-three minute time a month later with 2:58.0. In October 1937 Waalberg improved her own world record for a third time, swimming 2:56.9. A year later at the 1938 European Aquatics Championships in London she won bronze in the 200 metres breaststroke.