The scouting party got back to Oxley's encampment at Mt. Harris on 18 July 1818. On the same day, Oxley named the river in honour of the British Foreign Secretary, Lord Castlereagh, who had been in that role since 1812. The whole group then departed the following day for the river that George Evans had crossed, heading in the same north-easterly direction that Evans had taken. On 27 July 1818 they reached the Castlereagh, but the land they traversed to get there was flooded, whereas it had not been flooded two weeks earlier on Evans's scouting trip. The Castlereagh itself was running high, and they were not able to cross it for another six days.
