The story of Ngurunderi and Pondi is one of the oldest pieces of literature on the continent, and versions of it stretch across the enormous span of the Murray system. The Ngarrindjeri around Lake Alexandrina tell of Ngurunderi paddling his bark canoe in pursuit of the cod, who carved each weaving bend and branching tributary in its desperate flight, until the chase ended near the lake and the great fish was finally caught and cut into the many species that swim the river still. Far upstream, the Wotjobaluk people of Victoria tell their own version, of the hero Totyerguil chasing the cod Otchtout from the country near Swan Hill. For one of the major rivers of the driest inhabited continent, such cultural weight is no surprise. The Murray was, and is, life itself.

The Murray's geological story is a saga of upheaval. Between 2.5 million and half a million years ago, the river didn't reach the sea at all; it drained into Lake Bungunnia, a vast inland freshwater sea covering 33,000 square kilometres, formed when earth movements dammed the river. When the lake finally drained around 600,000 years ago, it marked the end of a wet age and the onset of the dry conditions Australia knows today. Even more striking is the Cadell Fault. About 45,000 years ago the ground heaved upward along this line, and the Murray, blocked, split and detoured around it. The chaos of redirected channels and regular flooding it created was perfect for one tree, the river red gum, which rose into the magnificent Barmah forests that still line the river, born directly from an ancient earthquake.

When Europeans arrived they could not even agree on what to call it. Hamilton Hume and William Hovell crossed it near present-day Albury in 1824 and named it the Hume, after Hume's father. Six years later Charles Sturt, having floated down the Murrumbidgee, reached the same water and named it the Murray for a British colonial secretary, never realising it was the river Hume had already found upstream. Sturt rode it all the way to Lake Alexandrina and the sea. The Murray went on to become a border too, dividing New South Wales from Victoria along the top of its southern bank, a boundary so legally peculiar that in 1980 the High Court of Australia had to rule on which state held jurisdiction over a man who died fishing from the Victorian edge.

For roughly seventy years, the Murray was a working highway. The first paddle steamers churned upstream on the spring flood of 1853, the Lady Augusta reaching Swan Hill and the Mary Ann pushing toward Echuca, and within a decade dozens of shallow-draught steamers and barges worked the river in the high-water season. Echuca became Victoria's second port, shipping the wool clip of the Riverina down to Melbourne. It was never easy water. The river was choked with "snags," whole drowned trees that could tear a hull open, and crews fought them with steam-winched barges. The unreliable, shifting levels eventually doomed the trade once railways reached the river. Today the paddle steamers carry tourists, not wool, but the great wooden boats still turn their wheels on the same brown water their ancestors did.

The modern Murray is plumbed, locked, and fought over. From 1915 the three Murray states agreed to build storage dams, and a chain of locks and weirs followed, while barrages near the mouth hold back the sea. The river was inverted: its natural winter-spring floods and summer dry were reversed to keep water flowing for irrigation, making the Murray Valley the nation's most productive farmland and supplying 40 percent of Adelaide's drinking water. The cost has been heavy. Salt is rising through the soil, European carp have wrecked native habitat, the red gum forests have suffered through brutal droughts, and at the very end the Murray Mouth would silt shut and strangle the Coorong's lagoons were it not dredged 24 hours a day. The river that a cod once carved now depends on machines to reach the sea. Saving it remains one of Australia's hardest and most urgent tasks.