Dangar Island has been known to the local Guringai Aborigines for thousands of years. The first European to visit the area was Governor Arthur Phillip, who explored the lower river by small boat in March 1788 within weeks of the First Fleet's arrival. He named it Mullet Island, for the abundance of fish in the local Hawksbury River. At first the local people were friendly towards him, but when he returned a year later, they would not come into contact. By 1790, over half the Guringai people had succumbed to the smallpox the British had brought with them.