From the Amazon to rivers flowing through India, an invisible crisis may already be unfolding beneath the surface. According to new research, rivers around the world are slowly being starved of oxygen — a change scientists say could disrupt aquatic life, weaken biodiversity and alter the health of freshwater ecosystems in the decades ahead.
A study published in Science Advances found that nearly 80 per cent of the world’s rivers have experienced declining oxygen levels over the last four decades, with climate change emerging as the biggest driver of the trend.
The research, led by Prof. Kun Shi of the Nanjing Institute of Geography and Limnology (NIGLAS) at the Chinese Academy of Sciences, analysed data from more than 21,000 river stretches across the globe collected between 1985 and 2023.
The findings paint a troubling picture: river oxygen levels declined at an average rate of 0.045 milligrams per litre per decade, while nearly 79 per cent of rivers studied showed signs of deoxygenation. For rivers, oxygen is not just important — it is essential for survival, ScienceDaily reported.
Dissolved oxygen helps sustain fish, aquatic organisms and biodiversity while supporting the natural biological processes that keep rivers healthy. When oxygen levels drop too far, rivers can struggle to support life, sometimes triggering conditions known as hypoxia, where aquatic species begin to suffocate.
But perhaps the biggest surprise in the study was where the damage appears to be worst. Scientists expected colder regions closer to the poles — where temperatures are rising rapidly — to face the steepest oxygen losses. Instead, tropical rivers between 20° North and 20° South latitude, including rivers in India, emerged as the most vulnerable.
Researchers believe tropical rivers are at greater risk because they naturally carry lower oxygen concentrations, leaving them with less room to cope as warming intensifies.
The study also found that heatwaves are accelerating the problem.Extreme heat events accounted for nearly 23 per cent of global river oxygen loss, while warming-driven reductions in oxygen solubility — the ability of water to hold oxygen — explained nearly 63 per cent of the overall decline.
In simple terms: warmer rivers hold less oxygen. “Climate warming is increasingly reshaping freshwater ecosystems,” the researchers noted, adding that tropical rivers should become a priority for conservation and climate adaptation measures.
The team also explored whether dams and river flow influence oxygen loss. Interestingly, shallow reservoirs created by dams appeared to worsen oxygen decline, while deeper reservoirs sometimes slowed the process. Both unusually low and high river flow conditions showed slightly lower oxygen losses compared to normal flow conditions.
Although the changes are happening gradually, scientists say the consequences could become increasingly visible — from declining fish populations to disruptions in freshwater systems that communities rely on for food, farming and drinking water.
For now, the warning from researchers is clear: the climate crisis may not only be warming rivers — it may also be quietly taking their breath away.
