The McArthur gathers itself on the northern edge of the Barkly Tableland and runs north and east toward the sea, draining a basin of just over 20,000 square kilometres. It is fed by creeks and rivers with names like Tooganginie, Kilgour and Clyde, and it pushes some 3.27 million megalitres of water seaward in an average year — most of it in the wet, when the headwaters that trickle in the dry become a roar. In its upper reaches the river has cut spectacular gorges through ancient sandstone. Lower down it slows, spreads and turns tidal, the freshwater giving way to a long saltwater estuary that reaches all the way inland to the town of Borroloola.

For the peoples of this country, the entire river is sacred — not a backdrop to sacred sites but a living one. It is the road the Rainbow Serpent travelled, and there are places along it where the great snake is said to have risen from the ground. Not far off lie the Barramundi Dreaming and the Jabiru Dreaming, the country threaded with the deeds of ancestral creatures that are also the animals still living in it. To hold this knowledge is to hold law and responsibility together. The river is read, sung and cared for as kin, and that relationship long predates — and outlasts — any line a surveyor has drawn across it.

Beneath that sacred bend lies one of the largest zinc, lead and silver deposits on Earth. Underground mining began at the McArthur River Mine in 1995. To reach more of the ore, the operation proposed turning open-cut — which meant diverting the river itself, roughly five and a half kilometres of it, away from a place tied to an important Snake Dreaming. Traditional owners warned of damage that would be serious, lasting and impossible to undo. The courts agreed at first: in 2007 the Northern Territory Supreme Court found the approval invalid, and in 2008 the Federal Court ruled the expansion illegal.

Then, in early 2009, the federal environment minister Peter Garrett — once a protest singer himself — formally approved the expansion, attaching conditions meant to protect the freshwater sawfish and the migratory birds that depend on the estuary. The diversion went ahead. The river now runs where the mine needed it to, and the deposit it once covered is an open pit. Estimates suggest the site will need monitoring for a thousand years after mining ends to manage the heavy metals it leaves behind. For the families whose Dreaming runs through that ground, no condition on a permit can put back what the diversion moved aside.

Downstream of the controversy, the McArthur still arrives at the Gulf in remarkable health. Its estuary is rated near-pristine and forms part of the Port McArthur Tidal Wetlands, recognised internationally as an Important Bird Area. The river empties opposite the Sir Edward Pellew Group of Islands, the saltwater heart of Yanyuwa country, where mangroves give way to seagrass beds grazed by dugong and turtle. Here barramundi run and crocodiles wait, and the same water that was bent inland flows out, at last, to the sea the Yanyuwa call their spiritual home.