Global Rivers Are Losing Oxygen as the Climate Warms

Rivers are experiencing a decline in dissolved oxygen levels. Photo by Matt Benson on Unsplash.

Rivers around the world are losing dissolved oxygen, an essential condition for healthy freshwater ecosystems. A 2026 study published in Science Advances analysed 21,439 rivers across the world using more than 3.4 million satellite images from 1985 to 2023 and found that 78.8% experienced declining dissolved oxygen levels. Globally, river oxygen declined at an average rate of 0.045 milligrams per litre per decade. 

Dissolved oxygen supports fish, aquatic plants and microorganisms and helps maintain water quality and healthy river ecosystems. The study found that warming is the main driver of this decline, because warmer water holds less oxygen. Heatwaves can make the problem worse and have contributed to 22.7% of global river deoxygenation over the study period. 

What is Happening 

• Most rivers are losing oxygen: 78.8% of the 21,439 river studied experienced declining dissolved oxygen between 1985 and 2023. 
• Tropical and subtropical rivers are most affected: More than 60% of rivers between 30°S and 30°N showed significant declines, with a group of these rivers, exceeding 90% between 20°S and 20°N. 
• Some regions are seeing much faster declines: South America had the largest overall decrease, with 86.4% of river length showing declining oxygen. India also recorded some of the strongest declines. 
• Heatwaves accelerate oxygen loss: The study estimates that heatwaves contributed 22.7% of global river deoxygenation over the past four decades. 
• Dams can affect oxygen levels: dam impoundment can alter oxygen trends (according to the study), with shallow reservoirs generally experiencing greater deoxygenation. More than 50,000 damscurrently affect major river systems worldwide. 
• Future warming could make the problem worse: By the end of the century, global river dissolved oxygen concentrations are projected to decline by 1.1% under a low emissions scenario and 4.7% under a very high emissions scenario. Some regions, including India, the southeastern United States and the Paraná Plateau, could experience declines exceeding 12% under the highest warming scenario. 

Global Rivers Are Losing Oxygen: Why This is Getting Worse 

A warmer climate is increasing water temperatures and changing rainfall and river flows. Thus, as water gets warmer, it cannot hold as much oxygen. Warmer conditions can also speed up the activity of plants and microorganisms, which use more oxygen, thus, leaving less of it available for fish and other aquatic life. Furthermore, rainfall variability alters river flows, and lower river flows can reduce mixing and oxygen replenishment. 

Climate warming can also increase the frequency and intensity of heatwaves, creating short periods of rapid oxygen loss.

Other pressures, including dams, nutrient pollution and changes in river flow and land use, can interact with warming and further affect oxygen levels. This means climate change is adding pressure to rivers that may already be stressed by human activity.

The Arctic is warming nearly four times faster than the global average, changing the temperature difference between the Arctic and lower latitudes. This can influence the jet stream, the high altitude winds that steer weather systems, and contribute to persistent heat, rainfall or dry conditions in some regions. Such changes can intensify heatwaves and extreme rainfall, adding further stress to rivers through warmer water, low flows or sudden runoff. 

What This Means for People 

• Fish and biodiversity: Low oxygen can make rivers unsuitable for oxygen-dependent species and increase the risk of fish kills and biodiversity loss. 
• Water quality: Severe oxygen loss can contribute to poor water quality and damage the ecological functions that rivers provide.
• Food and livelihoods: Declining river health can affect freshwater fisheries and communities that depend on them.
• Drinking water: Healthy oxygen levels are an important indicator of freshwater quality, and degraded rivers can increase pressure on water treatment systems. 
• Ecosystem services: Rivers provide clean water, support fish and other aquatic life, recycle nutrients, and help sustain agriculture, livelihoods and local economies.

The Urgent Response Needed 

What Needs to Change:

• Monitor river oxygen: Expand continuous monitoring of dissolved oxygen, temperature and water quality.
• Reduce warming: Limit carbon pollution that is driving rising water temperatures.
• Protect river ecosystems: Restore wetlands, riparian vegetation and natural river flows.
• Reduce pollution: Reduce the amount of sewage, fertilisers, and other organic matter entering rivers. These pollutants can increase the growth and activity of microorganisms that use up oxygen, leaving less oxygen available for fish and other aquatic life.
• Manage dams carefully: Consider downstream oxygen levels and ecological impacts when operating and planning dams.
• Prepare for heatwaves: Use temperature and oxygen monitoring to identify rivers at risk of rapid oxygen loss.

What YOU Can Do: 

• Protect rivers: Keep plastics, chemicals and other waste out of waterways. 
• Save water: Reducing unnecessary water use can help protect stressed freshwater systems. 
• Follow local water advice: Pay attention to warnings about poor water quality, heat and pollution. 

Read more: Water Insecurity | Health risks | Climate Risks Daily 

Original source: https://www.science.org/doi/10.1126/sciadv.aef3132