Yamma Yamma is a lake that keeps time in decades. It fills to capacity only about once every 25 to 30 years, the most recent brimming coming in 2000, and in the long intervals between it lives a second life as country. The cracking clay soils carry extensive grasslands dominated by rat's tail couch, and after rain a scatter of ephemeral forbs greens the gaps between the tussocks. Along the north-eastern shore, open lignum shrubland gives way to patches of woodland where coolabah and belalie hold the line against the desert. The water itself is a creature of change. It arrives fresh off the Cooper, sweet enough to drink, and then, as months of sun pull it back into the air, it turns slowly saline, concentrating its salts until the basin dries to clay once more.

The lake carries a second name, Lake Mackillop, though the doubled Yamma Yamma is the one that sticks, a repetition that rolls off the tongue and lodges in the memory. It lies deep in the South West Queensland outback, on the Cooper Creek floodplain that the Channel Country is named for, far from any town of consequence. Birdsville sits well to the west, Windorah to the east, and between them stretches a country of gibber, grass and channel that swallows distance. Yamma Yamma is the largest inland ephemeral lake in the state, but for most visitors and most years it is simply a great pale plain. Only the cracked polygons of the clay and the bleached remains of past high-water lines hint at the lake that sleeps beneath the grass, waiting for the Cooper to wake it.

When the lake is full, the response is extraordinary. BirdLife International recognises Lake Yamma Yamma, together with its claypans and the nearby Barrolka Lakes, as an Important Bird Area of 1,218 square kilometres, because it has carried more than one percent of the entire world population of three species at once: plumed whistling-ducks, sharp-tailed sandpipers, and Australian pelicans. On an island at the north-eastern end, a great colony of pelicans nests, their chalk-white plumage stark against the brown water. The Barrolka Lakes hold colonies of cormorants. Hardheads, grey teal, glossy ibis, white-headed stilts, whiskered terns and Pacific black ducks crowd the shallows in their thousands, with rarer freckled ducks and white-winged black terns threaded among them.

How birds find a lake that appears once in a quarter-century, somewhere in the emptiness of inland Australia, is one of the quiet wonders of this country. They come from the coasts and from across the continent, some of the migratory waders having flown from breeding grounds in the Arctic, converging on a pulse of water that will not last. The flood that fills Yamma Yamma is the same flood that, in the biggest years, pushes all the way down Cooper Creek toward Kati Thanda-Lake Eyre. The lake is a single bright link in that vast, intermittent plumbing, a place where the boom-and-bust rhythm of the Lake Eyre Basin is written large, and where life waits, dormant in seed and egg, for the rivers to run.