Käthe Seidel (1907-1990) was a German botanist. Seidel was the first researcher to incorporate vegetation into wastewater treatment wetlands, beginning in the 1950s. She was nicknamed "Bulrush Kate" ("Die Binzen Kaethe") for her use of the common bulrush, Schoenoplectus lacustris. For many years, she led the Limnological Station of the Lower Rhine (Limnologische Station Niederrhein) based in the city of Krefeld. Focusing on studies of the Lower Rhine, the Limnological Station was associated with various institutions that became part of the Max Planck Society.