John Oxley, Surveyor-General of New South Wales, set out in 1817 to discover the course of the Lachlan River. Following the river downstream past the present site of Forbes, he found that it flowed into marshland and, unable to proceed further, decided to strike out for the South Australian coast. Shortage of water forced his return to the Lachlan, which he rejoined below the marshes previously encountered, but only to meet more marshland further on. Oxley decided to turn back and, leaving the Lachlan, crossed the Bogan River and followed the upper waters of the Macquarie back to Bathurst. In 1818, Oxley led an expedition to investigate the Macquarie River, but again marshland impeded the progress of his party. Considering this to be the termination of the river, he marched eastward and reached Port Macquarie, having discovered the Castlereagh and Peel Rivers and the rich and fertile Liverpool Plains.