The Woronora River rises on the northwestern slopes of the Illawarra escarpment and has its origin from Waratah Rivulet, near Darkes Forest, and flows generally north for approximately, joined by three minor tributaries, before reaching its confluence with the Georges River, between Como and Illawong. The total catchment area of the river is approximately and the area is generally administered by the Sydney Catchment Authority in its upper reaches and the Sutherland Shire Council in its lower reaches. Much of the course of the river is through the Dharawal State Conservation Area, Heathcote National Park and the Royal National Park as it descends from source to mouth. The river is impounded by the Woronora Dam, opened in 1941. The impoundment is Lake Woronora, formed to augment water supply for southern Sydney and the northern Illawarra region. The Woronora River is traversed by high level and low levelroad bridges and a footbridge in the suburb of Woronora. A road bridge on Heathcote Road, linking Heathcote and Holsworthy also provides a crossing over the river. At the area known as "The Needles", near Woronora Road in, a footbridge links the suburb to Barden Ridge. Comment from an ex resident: "The Needles" were considered the "head of navigation" where there was relatively deep water with pointed vertical rocks, mostly just below the surface, hence the name. There was a causeway there which was part of "The Old Illawarra Rd". This area is below the Heathcote Rd bridge by about 3/4 km. Just above this road bridge was "Woronora Wier" which was demolished in the mid 1900s for safety reasons.
Etymology
In the Australian AboriginalDharug language the river draws its name, meaning "black rocks". 'Woronora' is an Aboriginal place name. Records show the spelling of the name has varied since it first appeared in the 19th century, the earliest being Wooloonora. The name was first applied to the Woronora River, a tributary of the Georges River, before being given to an electoral district, a local road east of the river, and finally the suburb itself.