The headwaters of the Nepean River rise near Robertson, about south of Sydney and about from the Tasman Sea. The river flows north in an unpopulated water catchment area into Nepean Reservoir, which supplies potable water for Sydney. North of the dam, the river forms the western edge of Sydney, flowing past the town of Camden and the city of Penrith, south of which flowing through the Nepean Gorge. Near Wallacia it is joined by the dammed Warragamba River; and north of Penrith, near Yarramundi, at its confluence with the Grose River, the Nepean becomes the Hawkesbury River.