Global River Oxygen Levels Are Falling Rapidly Due to Climate Change, Study Warns

Discover why rivers worldwide are losing oxygen at an alarming rate. A new study links climate change to this silent crisis, with tropical rivers most at risk. Learn about the impact on aquatic life.

Scientists have warned that rivers around the world are slowly losing oxygen due to climate change, as revealed by a new study published in the journal Science Advances. The research shows that oxygen levels are dropping in most river systems globally, with tropical rivers being the most affected. Experts emphasize the need for immediate action to slow this decline and safeguard freshwater ecosystems.

The study was led by Professor Kun Shi from the Nanjing Institute of Geography and Limnology, part of the Chinese Academy of Sciences. Dr Qi Guan was the first author, and researchers from Tongji University also played a role in the project.

Why Oxygen Matters

Dissolved oxygen is vital for the health of rivers. It enables fish and other aquatic species to live, supports a wide range of life, and helps maintain key natural processes in water. When oxygen levels drop too low, river ecosystems begin to struggle, and freshwater species become more at risk.

To track changes in oxygen levels over time, researchers used a machine-learning stacking algorithm to analyze data from 21,439 river sections worldwide, collected between 1985 and 2023.

Their findings revealed a clear pattern of decreasing oxygen levels. On average, river oxygen levels fell by 0.045 milligrams per litre every decade, and nearly 79 per cent of the rivers studied showed signs of oxygen loss.

Tropical Threat

The biggest drops in oxygen were seen in tropical rivers located between 20 degrees south and 20 degrees north, including rivers in India. This was unexpected, as scientists had thought colder regions, where warming is more intense, would be more at risk.

However, the researchers found that tropical rivers already have lower natural oxygen levels, making them more vulnerable to further decline. The faster loss of oxygen in these areas also increases the risk of hypoxia, a condition where oxygen levels become too low to support aquatic life.

Climate Impact

The study also looked at how river flow, dams, and heatwaves affect oxygen loss. Both unusually low and high river flows seemed to slightly reduce oxygen loss compared to normal conditions. Shallow dams increased oxygen loss, while deeper reservoirs helped slow it down.

Researchers concluded that rising temperatures were the main cause of the global oxygen decline, accounting for 62.7 per cent of the loss. Heatwaves alone contributed 22.7 per cent and made oxygen loss even worse. The team stressed that these findings offer important scientific evidence for policymakers and highlight the urgent need to focus on tropical rivers in future climate and conservation strategies.