The Nepean Dam is a heritage-listed dam split across Avon in the Wingecarribee Shire and Bargo in the Wollondilly Shire, both in New South Wales, Australia. The reservoir created by the dam spreads across Avon, Bargo and also Yerrinbool in Wingecarribee Shire. The Nepean Dam is one of four dams and weirs in the catchment of the Upper Nepean Scheme, in New South Wales, Australia, and provides water to the Macarthur and Illawarra regions, the Wollondilly Shire, and metropolitan Sydney. Completed in 1935 under the supervision of Ernest Macartney de Burgh, the dam is currently managed by the Sydney Catchment Authority and is listed on the New South Wales State Heritage Register.