It 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 level
road 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. "The Needles" is considered the "head of navigation" where there is relatively deep water with pointed vertical rocks, mostly just below the surface, hence the name. Until 2008, there was a vehicle causeway there at an area called the Pass of Sabugal, so named by Major Mitchell who surveyed the route in 1843 for what would become part of Old Illawarra Road. The causeway was modified in 2008 to allow the passage of fish and so is now unsuitable for vehicular traffic but still suitable for pedestrians or cyclists. The Needles area is downstream of Heathcote Rd bridge by about 3.4 km. Just above the Heathcote Rd bridge was "Woronora Wier" which was demolished pre-1994 and the roadside parking area removed for safety reasons. ==Etymology==