The world's oceans, lakes and rivers are slowly losing oxygen. Scientists call this aquatic deoxygenation. It is happening gradually, so many people don't notice it. But a new study by researchers at UC San Diego's Scripps Institution of Oceanography says this is becoming a serious global problem. The researchers believe it should be treated with the same urgency as climate change and biodiversity loss. A new study out of UC San Diego's Scripps Institution of Oceanography says it's time to stop treating this as a side issue and start treating it as one of the defining threats to the planet's stability.

The paper, published in Limnology and Oceanography, isn't built around some dramatic new measurement. It's more of a stock-take — pulling together research that's mostly existed in separate silos until now. Ocean oxygen dropping in one field. Rivers running low during heatwaves, studied by someone else entirely. Lakes losing their deep-water oxygen reserves, a third group's problem. The Scripps team's contribution was mostly to ask: what happens when you look at all of this together, instead of as isolated case studies?

Dissolved oxygen doesn't get talked about much outside science circles, but it's the thing keeping most life underwater alive — fish, plankton, shellfish, sharks, the whole chain. Take it away, even partially, and the effects show up fast. Erica Ferrer, who led the study during her PhD at Scripps and is now doing postdoctoral work at UC Santa Barbara, says the planet's overall health is basically tied to how healthy these aquatic systems are, and right now that connection isn't getting the attention it deserves.

So what's actually causing the drop? A few things, none of them shocking on their own. Warmer water simply can't hold as much dissolved oxygen — that's basic chemistry, and as oceans and rivers heat up, this happens automatically. Then there's nutrient pollution, mostly runoff from farms and wastewater, which feeds algae blooms; when those blooms die off and decompose, they suck up huge amounts of oxygen and leave behind what scientists bluntly call dead zones. And changes in ocean circulation — how well surface water mixes with the depths — make it harder for oxygen to reach where it's needed. None of these is the whole story by itself. Together, they add up to something much worse.

It's not just fish that suffer either. Whales, seals, dolphins — animals that breathe air at the surface — still get hit, because their prey moves or disappears, their habitats degrade, and the food webs they've relied on for generations start falling apart underneath them.

Here's where the study gets more pointed. Back in 2009, scientists came up with something called the planetary boundaries framework — nine processes considered essential to keeping Earth stable, things like climate change, biodiversity loss, ocean acidification, freshwater change. The framework tracks how close humanity is to pushing each one past a safe limit. Dissolved oxygen was never included as one of the nine. Ferrer and her co-authors think that's a mistake, and their paper spends most of its length making the case — going boundary by boundary, showing how oxygen loss feeds into nearly every other crisis already on that list, and gets fed by them in return. Warming drains oxygen from water. Less oxygen makes warming's other effects worse. Pollution drains oxygen. Low oxygen makes pollution's damage spread further. It's not a straight line of cause and effect — it's a loop, tangled in on itself, which is exactly why the researchers think it's been so easy to overlook.

The idea for the paper apparently traces back to 2019, when Ferrer and senior author Lisa Levin, a Scripps biological oceanographer, both went to COP25, the UN's climate conference in Madrid that year. Oxygen loss kept surfacing in conversations about climate and pollution and dying ecosystems, but never as its own topic — always tagging along behind something else. That's reportedly what got them thinking this deserved its own paper.

The study warns that some of the oxygen already lost from oceans, lakes and rivers may not return for hundreds of years, even if pollution and greenhouse gas emissions are reduced soon.

What the researchers actually want isn't a specific new policy or technology. It's recognition — getting aquatic deoxygenation formally added to that planetary boundaries list, so it gets studied and funded and legislated around with the same seriousness as climate change or biodiversity loss, instead of showing up as a footnote in papers about something else.

The study came out June 30, 2026. Alongside Ferrer and Levin, researchers from UC Santa Cruz, UCLA, the Institut de Physique du Globe de Paris, and Rensselaer Polytechnic Institute also contributed.

Click here to read more reports