The Clarence River is situated in northeastern New South Wales, Australia. The river originates on the watershed that marks the Queensland border. After flowing south and northeast for 394 km it then empties into the Pacific Ocean at Yamba/Iluka. On its journey it passes through the towns of Grafton, Ulmarra, Cowper/Brushgrove, Maclean and Harwood. Its chief tributaries are the Mann River, Nymboida River, and Orara River. The river features many large river islands, including Woodford Island, Chatsworth Island, and Harwood Island. The river supports a large prawn trawling and fishing industry.
The Clarence River system is an extensive East Coast drainage with many tributaries of differing size. Apart from the Murray River, it is the largest river in mainland Australia south of the Tropic of Capricorn, though its flow for comparison is only half that of the Potomac. Its basin is, together with the very similarly-sized Hawkesbury, Australia's largest Pacific watershed south of Bundaberg. The extremely intense rainfalls that typify the North Coast mean, however, that major floods can temporarily raise the flow of the Clarence to levels equivalent to some of the largest rivers in the world.
Most of the Clarence basin is heavily forested, with important areas of remnant subtropical and temperate rainforest occurring all along the course. Only in alluvial areas where soils are less leached is there major agricultural development: in these areas the chief industries are cattle rearing and the growing of sugar cane in lower-lying areas.
Of particular interest is the small island town of Harwood, where a Sperry New Holland factory and a quaint Bush Pub overlook the Clarence Delta. Harwood is also the location of the local sugar Mill, the Harwood Sugar Mill built in 1873 and is the oldest Australian mill still operational. The sugar mill is situated on the river due to its importance in transporting sugar cane from farms in the surrounding area in previous times. Harwood is just after the Yamba Bridge on part of Australia's National Highway from Sydney, Port Macquarie, Coffs Harbour to Brisbane.
The freshwater reaches of the Clarence River support important populations of native freshwater fish including Eastern freshwater cod, an endangered fish species unique to the Clarence River system, and Australian bass.
The lower half of the river valley is part of the Local Government Area of the Clarence Valley. The Aboriginal people of the lower reaches call the river there Breimba or Berrinbah.