Rivers around the world are steadily losing dissolved oxygen, with nearly 80% of river systems showing signs of deoxygenation over the past four decades, according to a major new study published in Science Advances.
The research, led by Prof. Kun Shi of the Nanjing Institute of Geography and Limnology at the Chinese Academy of Sciences, analysed observations from 21,439 river systems worldwide collected between 1985 and 2023 using a machine-learning algorithm. River oxygen levels declined at an average rate of -0.045 mg per litre per decade across the study period.
Dissolved oxygen is critical to healthy river ecosystems, supporting aquatic organisms, sustaining biodiversity and driving important biogeochemical processes. When levels fall, fish and other freshwater species face significant risk.
The findings challenge previous assumptions about which rivers are most at risk. Tropical rivers, located between 20°S and 20°N, showed the strongest oxygen losses, outpacing even rivers in rapidly warming polar regions.
Researchers say tropical rivers already tend to have lower oxygen concentrations, making them especially vulnerable to further decline and increasing the likelihood of hypoxia events where oxygen becomes too scarce to support aquatic life.
Climate warming was identified as the primary driver, accounting for 62.7% of observed oxygen decline through reduced oxygen solubility.
Heatwave events contributed a further 22.7%, accelerating deoxygenation rates significantly compared with average temperature conditions. Ecosystem metabolism accounted for 12% of the decline.
The study also found that dam impoundment produced mixed effects, with shallow reservoirs accelerating oxygen loss while deeper reservoirs helped reduce deoxygenation in impounded areas.
Researchers say tropical rivers should be treated as a top priority for mitigation efforts, and that the findings provide a scientific foundation for policymakers developing strategies to address river deoxygenation worldwide.
Copyright © 2026 Energy Live News LtdELN