The Nepean Dam is a heritage-listed arch dam across the Nepean River; it is tall and long. Construction on the Dam began in 1926, construction was delayed for two years during the Depression, it was finally completed in 1935. The capacity is listed variously as . The Nepean Reservoir has a small storage capacity in relation to its large catchment area of . While its capacity is much the same as that of Cataract and Cordeaux Reservoirs, its catchment basin is two and a half times as extensive as Cataract and three and a half times as extensive as Cordeaux. The Nepean Reservoir therefore fills more rapidly and, under normal conditions, is drawn upon more freely than the other reservoirs. The dam is located at an elevation of above sea level and the construction cost was A£2,062,000.