In a tributary of the Reconquista River outside Buenos Aires, the waterline has dropped far enough to expose banks of grey sediment that locals say they have never seen before. That image captures a finding that scientists are now measuring at a planetary scale: according to a new report from the World Meteorological Organization, rivers across the world experienced one of the driest years in more than three decades during 2025. The statistic lands quietly, but its implications stretch across every continent where a river feeds a city, irrigates a crop, or sustains a delta ecosystem. The pressures are not uniform, but they are cumulative.

In Latin America, both the Amazon — whose name in several indigenous traditions translates roughly as "the river that swallows all rivers" — and the La Plata system have been hit by prolonged drought. In South Asia, shifts in the timing and intensity of the annual monsoon have disrupted the Ganges and the Brahmaputra, two rivers whose seasonal rhythms have organised human settlement for millennia. Further south and west, even the Congo — the world's deepest river, which crosses the equator twice on its path to the Atlantic — has been drying slowly for decades, driven by reduced rainfall, a weakening of the Walker circulation, and rising sea-surface temperatures in the central-eastern tropical Atlantic. What makes the situation harder to reverse is that almost none of these rivers run free.

From source to sea, most of the world's major waterways have been engineered, dammed, and diverted. Political contests over water allocation are intensifying: the Colorado River is disputed between American states, while Egypt and Ethiopia have only recently begun to settle their long-running standoff over the Nile.