Middle Harbour (or Warrin ga[1][2]), a semi–mature tide dominated drowned valley estuary,[3] 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.

There are many small creeks draining the surrounding hills, but no significant rivers flow into Middle Harbour.

Much of the rugged shore of the Middle Harbour remains covered with bushland, most of it now protected by parks and reserves.

An example of the cultural significance of Middle Harbour is highlighted through an odd custom amongst boaters who use the Tunks Park boat ramp in Cammeray.

Becoming popular in the late 1980s and 1990s, boaters exiting the 4 knot zone outside of the Cammeray Marina would play "The Old Man Down The Road", a swamp rock song written by Creedence Clearwater Revival lead singer and guitarist, John Fogerty, on their cassettes.