Stand on the bank of almost any river on Earth, and the water looks the same as it always has. But something invisible is changing beneath the surface. Slowly, almost silently, the world's flowing waters are losing the oxygen that keeps them alive.
A sweeping new study published in May 2026 examined over 21,000 river sections across the globe, using nearly four decades of data. The result was striking: almost four out of every five rivers showed signs of losing oxygen. Dissolved oxygen is the gas that fish, insects, and other aquatic creatures need to breathe. Warmer water holds less of it. When oxygen drops too low, fish can die and rivers become lifeless.
The main cause is the warming climate. As temperatures rise, water cannot carry as much oxygen. This single factor accounted for roughly 63% of the observed change. The worst losses appeared in tropical regions, where rivers already have lower oxygen levels and little room to spare.
India's rivers were among the most affected. The Ganges, the sacred river that supplies water to hundreds of millions of people in northern India, was losing oxygen more than twenty times faster than the global average. In a river system already burdened by heavy pollution, warming makes the problem worse.
The research, led by Professor Kun Shi of the Nanjing Institute of Geography and Limnology, used advanced computer technology to study oxygen levels across thousands of river segments. Under future climate projections, rivers across the Eastern United States, the Arctic, India, and South America are expected to lose about 10% of their oxygen by 2100. The losses are small, but for creatures that depend on every breath the water gives, they mean the difference between a living river and a dying one.