Middle Harbour (or Warring-Ga), a semi–mature tide dominated drowned valley estuary, is the northern arm of Port Jackson, an inlet of the Tasman Sea located north of Sydney central business district on the coast of New South Wales, Australia.Middle Harbour has its source in the upper reaches of Garigal National Park where it forms Middle Harbour Creek and flows southeast to become Middle Harbour at Bungaroo and travels for approximately 10 kilometres (6.2 mi) before reaching its mouth at Port Jackson between Grotto Point near Clontarf and Middle Head.The catchment area of Middle Harbour is approximately 100 square kilometres (39 sq mi).