Wanting to join the women’s swimming club in Amsterdam, HDZ, the 13-year-old Beisenherz was barred for being too young. With several other rejected girls, they founded their own club, later named Amsterdamsche Dames Zwemclub (ADZ). In 1920, Beisenherz won the first Dutch title for women, the 100 m freestyle, a feat she repeated in 1921 and 1922. This performance also earned her a ticket to the Antwerp Olympics, where she came up against the much better technique and faster starts of the American girls, but returned with a new Dutch national record and with the distinction of being the first Dutch female Olympian. Beisenherz also played for the water polo team of ADZ, although she never claimed a Dutch title. At the 1920 Olympics, she participated in an all-Dutch water polo demonstration event, 80 years before the women’s event would be on the official Olympic Program.
Netherlands