The Clarence is the largest river on the East Coast of NSW, with a catchment area of 22,660 square kilometres, with a population of some 70,000.

It flows for over 400 kilometres, from its northern boundary, the McPherson Range on the Queensland boarder, to the sea. The western boundary is the Great Dividing Range, near Stanthorpe and Glen Innes, and in the south, the Bald Blair and Doughboy Ranges and the Dorrigo Plateau. Near the coast, the Richmond Ranges north of Iluka, separate the Clarence catchment from the Richmond. Similarly, the coastal ranges from Coffs Harbour to Yamba separate the Clarence catchment from the narrow coastal strip around Coffs Harbour.

Approximately 33% of the catchment is mountainous or rugged, 33% steep to hilly, 17% undulating to hilly, and 17% mostly flat. The tidal reaches of the lower Clarence meander through 530 square kilometres of floodplain that extends upstream as far as Copmanhurst. The coastal floodplain has 100 km of levees, 166 km of drains and watercourses, and 300 floodgate structures that were all built for flood mitigation.

There are 6 primary tributaries of the Clarence River namely, the Cataract, Timbarra, Mann, Orara, Guy Fawkes, and the Nymboida Rivers. Of these tributaries, all but the Orara have head water zones comprised of steep streams with gorges and confined valley settings. There are also 3 coastal sub catchments that are independent of the Clarence River and drain directly to the sea. These are the Angourie subcatchment, and the Sandon and Wooli Rivers.