Study Warns 80% Of World's Rivers Losing Oxygen

Rivers across the globe are quietly running low on oxygen, and the trend is accelerating. A new analysis of satellite and climate data shows that nearly 80% of the world's rivers have seen dissolved oxygen levels decline since 1985. This trend threatens fish, aquatic insects and the communities that depend on freshwater.

The research, led by environmental scientist Qi Guan at the Chinese Academy of Sciences and published in Science Advances, tracked oxygen in more than 16,000 rivers. The researchers used 3.4 million satellite images from 1985 to 2023, and found that on average, rivers lost 0.045 milligrams of oxygen per litre each decade.

Researchers expected high-latitude rivers to suffer most from warming, but the data point to the tropics instead. If emissions continue at current rates, the team projects that by 2100, rivers across much of South America, India, the Arctic, and the eastern U.S. could lose around 10% of their dissolved oxygen.

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Why is oxygen falling

Warm water holds less oxygen, and rising temperatures are only part of the story. Nutrient pollution from agriculture and wastewater fuels algae growth; when algae die and decompose, microbes consume even more oxygen. Dams and reservoirs slow water flow, giving those processes more time to deplete oxygen.

Scientists also warn that low-oxygen rivers can release greenhouse gases and toxic metals from sediments, creating feedback loops that worsen water quality.

"Deoxygenation is a very slow process. If we have a long period, the negative impact will attack the river ecosystems," Guan told Seth Borenstein at Associated Press.

"The low level of oxygen can cause a series of ecological crises such as biodiversity decline [and] water quality degradation."

"Systematically understanding these changes is crucial for enhancing the resilience of fluvial ecosystems to sustained deoxygenation risks through targeted measures and strategies, and helps to achieve sustainable management in global rivers," Guan and team conclude.