During 1789 Governor Phillip and some of his officers began to explore the country surrounding the main camps at Sydney Cove and Rose Hill, and northwards along the eastern coast. In March Phillip explored Broken Bay, and in June he discovered the mouth of the Hawkesbury River. In a dispatch to Lord Sydney he described his excursion:

After having been several times with the boats to Broken Bay, in order to examine the different branches in that harbour, a river was found, but the want of provisions obliged us to return without being able to trace it to its source, which has since been done and in the sixteen days we were then out all those branches which had any depth of water were traced as the boats could proceed.

The river, which I named Hawkesbury, after the Lord Hawkesbury, is laid down in the chart from an eye-sketch made by Captain Hunter, as we rowed up it. The breadth of this river is from three hundred to eight hundred feet, and it appears from the soundings we had to be navigable for the largest merchant ships to the foot of Richmond Hill; but as the water near the head of the river sometimes rises, after heavy rains, thiry feet above its common level, it would not be safe for ships to go far up; but fifteen or twenty miles below Richmond Hill they would lay in fresh water and perfectly safe. I speak of Richmond Hill as being the head of the river, it there growing very shallow, dividing into two branches.

The high rocky country which forms Broken Bay is lost as you proceed up the Hawkesbury, and the banks of the river are then covered with timber, the soil a rich light mould, and judging from the little we saw of the country, I should suppose it good land to a very considerable extent; the other branches of fresh water are shoal, but probably run many miles further into the country than we could trace them with our boats. On these rivers we saw great numbers of wild ducks and some black swans; and on the banks of the Hawkesbury several decoys made by the natives for to catch the quail.

Richmond Hill (near the foot of which a fall of water prevented our proceeding further with the boats) is the southern extremity of a range of hills, which, running to the northward, most probably join the mountains which lay nearly parallel to the coast, from fifty to sixty miles inland. the soil of Richmond Hill is good and it lays well for cultivation. Our prospect from the hill was very extensive to the southward and eastward, the country appearing, from the height at which we were, to be a level covered with timber, there is a flat of six or seven miles between Richmond Hill and a break in the mountains, which separates Lansdown and Carmarthen Hills, and in this flat I suppose the Hawkesbury continues its course, but which could not be seen for the timber that, with very few exceptions, covers the country wherever the soil is good.

The great advantages of so noble a river, when a settlement can be made on its banks, will be obvious to your Lordship.

-A. Phillip to Lord Sydney, 13 February 1790, in Historical Records of Australia, series I, vol.-, pp. 155-6