Erwin Sietas (24 July 1910 – 20 July 1989) was a German swimmer who specialized in the 200 m breaststroke. He competed at the 1928, 1932 and 1936 Olympics and finished in fourth, fourth and second place, respectively. Sietas was known for his fast start; in 1932 and 1936 he led he race, but faded at the finish. He won three medals at the European championships, including a gold in 1934.
Between 1928 and 1936 Sietas won all national titles, and in 1935 set a world record in the 200 m breaststroke. He was the only European breaststroke swimmer to win an Olympic medal between 1928 and 1952. In 1992 he was inducted into the International Swimming Hall of Fame.