Complex sentence: Near Penrith it is joined by the Warragamba River; and north of Penrith, near Yarramundi, at its confluence with the Grose River, the Nepean becomes the Hawkesbury River.
Split into simpler sentences: Near Penrith it is joined by the Warragamba River. North of Penrith, at the junction of the Grose River near Yarramundi, the Nepean becomes the Hawkesbury River.