The Adelaide River is a river in the Northern Territory of Australia.
The river rises in the Litchfield National Park and flows generally northwards to Clarence Strait, joined by eight tributaries including the west branch of the Adelaide River, Coomalie Creek, Margaret River and Marrakai Creek, before discharging into its mouth in Adam Bay in the Clarence Strait. The river descends 151 metres over its 238-kilometre course. The catchment area of the river is 7,640 square kilometres.
The Adelaide River is crossed by both the Stuart Highway, adjacent to the township of Adelaide River, and the Arnhem Highway near Humpty Doo.
The Adelaide River is well known for its high concentration of saltwater crocodiles, along with other wildlife including white-bellied sea eagles, whistling kites, freshwater crocodiles, bull sharks and black flying-fox. Its lower reaches form part of the Adelaide and Mary River Floodplains Important Bird Area. Waters of this river are also home to endangered speartooth shark and critically endangered largetooth sawfish. The river also contains a notable introduced population of Siamese fighting fish.
