Middle Harbour extends about 10 kilometers (6 miles) to the northwest, from where it joins the main harbour near the Heads. Its shore are nearly everywhere rugged, barren and forested and for this reason Middle Harbour was almost entirely neglected during the first two centuries of European settlement in Sydney. There are only a few small patches of flat land on its shores. There are many small creeks draining the surrounding hills, but no significant rivers flow into Middle Harbour.
Middle Harbour is a significant physical barrier between Sydney and the suburbs known as the Northern Beaches area which lie north and east of Middle Harbour. There are only two bridges - the Spit Bridge and the Roseville Bridge. Because of this obstacle, historically the main transport between Manly and Sydney was by ferry.
Since the 1920s, most of the land on the ridge-tops around Middle Harbour have been developed for suburban housing. Much of the rugged shore of the Middle Harbour remains covered with bushland, most of it now protected by parks and reserves. Middle Harbour is a popular area for recreational boating and fishing.
Cook named the harbour after Sir George Jackson, Judge Advocate of the Fleet at the time; he noted in his log that "there appears to be a good anchorage".
Port Jackson is bridged by the SydneyHarbour Bridge and the ANZAC Bridge (formerly known as the Glebe Island Bridge).
One tunnel, the SydneyHarbour Tunnel passes underneath the Harbour, to the east of the bridge, and in 2005 it was proposed that a third harbour crossing, this time a railway line, be constructed to the west of the bridge.