Helena Elisabeth "Lenie" de Nijs (born April 1939) is a retired Dutch swimmer. In July-August 1955 she broke three freestyle world records over 1500 m, 880 yd and 1760 yd distances. She then changed to backstroke, winning three national titles over 100 m (1956–1958) and setting world records in the 200 m backstroke (1957) and 4×100 m medley relay events (1956 and 1958); she set her last record while winning the European title in Budapest, together with Ada den Haan, Cocky Gastelaars and Atie Voorbij. She qualified for the 1956 Summer Olympics, but could not participate due to the boycott of those games by the Netherlands.