Climate change is no longer threatening only the world’s oceans. A new scientific study has found that rivers across the globe are steadily losing oxygen, raising fresh concerns over the future of freshwater ecosystems and the communities that depend on them.
The research, published in the journal Science Advances, was led by scientists at the Nanjing Institute of Geography and Limnology under the Chinese Academy of Sciences. After examining nearly four decades of data from more than 21,000 river segments worldwide, researchers found a widespread and persistent decline in dissolved oxygen levels in rivers between 1985 and 2023.
The findings point to a growing environmental crisis that scientists say could reshape aquatic life in many parts of the world. Around 80 percent of the rivers included in the study showed declining oxygen concentrations, with average levels dropping by 0.045 milligrams per liter every decade.
For rivers, oxygen is not just a chemical measure. It is the foundation that sustains fish populations, aquatic insects, microorganisms and the broader ecological balance within freshwater systems. As oxygen levels fall, rivers become increasingly vulnerable to biological collapse, particularly during prolonged heatwaves and low-flow conditions.
Rising Temperatures Are Reshaping River Systems
Researchers identified global warming as the primary driver behind the decline. Warmer water naturally holds less oxygen, meaning rivers exposed to rising temperatures are gradually turning into low-oxygen environments.
Scientists warn that the consequences are already becoming visible in some regions. Fish mortality events, deteriorating water quality and disruptions to aquatic biodiversity are expected to intensify if warming trends continue unchecked.
The study also highlights how climate change is altering river behavior beyond temperature alone. Changing rainfall patterns, irregular water flow, prolonged droughts and sudden flooding are placing additional stress on freshwater ecosystems that are already under pressure.
Tropical Rivers Facing Greater Risk
One of the study’s most significant findings is that tropical rivers appear to be losing oxygen faster than previously expected.
Earlier assumptions suggested that colder or polar regions would face the most severe impacts from oxygen loss. However, the research found that rivers in South Asia, Africa and South America are experiencing particularly rapid declines.
Scientists believe higher temperatures combined with intense human pressure are accelerating the deterioration of river health across these regions.
In many developing countries, rivers are already burdened by untreated sewage, industrial discharge, agricultural runoff and excessive chemical pollution. These pollutants consume oxygen as they break down in water, worsening the decline caused by climate change itself.
More Than an Environmental Problem
Experts involved in the study say the issue can no longer be viewed only as an ecological concern. Declining river oxygen levels are closely tied to food security, drinking water quality and public health.
Millions of people rely directly on rivers for fisheries, farming and household water use. As river ecosystems weaken, the social and economic impacts are likely to spread far beyond environmental sectors.
Researchers argue that river protection must now become a central part of climate policy discussions rather than remaining a secondary conservation issue. Without stronger action to reduce emissions and control pollution, scientists warn that many rivers could face long-term ecological damage that may become increasingly difficult to reverse.