Earth's Oceans, Lakes and Rivers Are Losing Oxygen at an Alarming Rate, Scientists Warn

Oxygen is disappearing from the planet's oceans, lakes, rivers and coastal waters at an alarming rate, and scientists warn the trend is pushing Earth toward an "unsafe" zone with consequences that could last for centuries. The findings, published in the journal Limnology and Oceanography, argue that dwindling oxygen deserves to be treated as a planetary boundary as critical as carbon dioxide levels or biodiversity loss.

The study was led by Erica Ferrer, a postdoctoral scholar at the University of California, Santa Barbara, with Lisa Levin, a biological oceanographer at UC San Diego's Scripps Institution of Oceanography. Together they synthesized evidence that aquatic deoxygenation is accelerating across nearly every kind of water body, from the deep open ocean to shallow lakes.

The causes are largely human. Warming water holds less dissolved oxygen, so climate change alone is steadily draining aquatic systems. On top of that, excessive nutrient pollution — much of it fertilizer runoff from farms — fuels blooms of algae that consume oxygen as they decay, creating expanding "dead zones." Changes in how water circulates and ventilates its deeper layers compound the problem, trapping oxygen-poor water below the surface.

The consequences ripple through entire ecosystems. Low-oxygen conditions can suffocate or displace marine life, from microscopic organisms at the base of the food web to fish and sharks near the top. As habitats shrink or shift, prey for marine mammals becomes scarcer or moves elsewhere, unraveling food webs that took millennia to assemble.

Beyond the creatures that live in it, oxygen-starved water disrupts the biological and chemical processes that help regulate Earth's climate, including the cycling of carbon and nitrogen. That means deoxygenation is not only a symptom of a warming world but a force that can accelerate it, in a feedback loop that scientists are only beginning to quantify.

The researchers caution that some of these changes could become effectively irreversible within human lifetimes, and they call for oxygen loss to be monitored and managed with the same urgency as greenhouse gas emissions. Curbing nutrient pollution and slowing warming, they say, are the most direct levers available to keep the planet's waters breathable.