The river rises at the western end of a feature called China Wall on the Barkly Tableland, in the Northern Territory, and sets off southeast before turning hard to the east. It crosses the border into northwest Queensland near Nudjabarra, traversing wide, mostly uninhabited plains, then sweeps past the Shadforth Plain and the Aboriginal community of Doomadgee. Near the Tiranna Roadhouse it bends north, crossing Hann Crossing and slipping past Escott, just west of Burketown, where it joins its main tributary, the spring-fed Gregory River. From there the combined waters run north into Pasco Inlet and the Gulf of Carpentaria. The drainage basin spans some 53,200 square kilometres, split between two jurisdictions, with about 15,733 of those square kilometres lying on the Territory side of the line.

The country the river drains is the homeland of the Yukulta and Ganggalidda, Waanyi, Maga-Kutana, Wakabunga, Nguburinji, and Mingin peoples, who have lived here across uncounted generations. The Waanyi language, spelled variously as Wanyi, Waangyee, or Wanji, threads the western reaches of Lawn Hill Creek and the Nicholson, running from the Territory border westward toward Alexandria Station and Doomadgee. To call the river Ganalanga is to use the name carried in that language, a reminder that the river was mapped, named, and known in human speech long before any surveyor arrived to write a different word on a chart.

This is a river ruled by the sky. When cyclones spin in off the Coral Sea to the east or the Gulf of Carpentaria to the north, the rain they dump can turn the Nicholson into a force that reshapes the country, and its mean annual discharge already runs to a substantial 2,237 gigalitres. The great flood of 1971 swept through the entire catchment, and lesser inundations in 2000, 2004, and 2009 each cut the roads and isolated the communities along its banks. For the people of Doomadgee and the scattered stations, the river is both lifeline and hazard, the same water that sustains the dry months arriving, some years, all at once.

Few rivers carry a political border the way the Nicholson does. The line between the Northern Territory and Queensland is an arbitrary human invention, a meridian drawn on a map, and the river pays it no mind, carrying Territory rainfall into Queensland soil and on to a Queensland sea. The watershed sits hemmed in by neighbours, with the Robinson River and Settlement Creek catchments to the north, the Barkly River to the south, and the Leichhardt to the east, named for the very explorer who passed through and named the Nicholson in turn. Together these Gulf rivers form a loose family, draining one of the least-populated and least-altered corners of the continent.