Rivers, streams, lakes, and reservoirs—those shimmering arteries that wind through our landscapes—do more than add beauty to our world. They are alive in the truest sense: flowing, cycling, and breathing. Just like us, these inland waters take in and release oxygen, sustaining life within and beyond their banks. But a new, eye-opening study led by researchers at Utrecht University reveals a sobering truth: we’ve been slowly choking these waters for over a century. Welcome to the Anthropocene—the age of humans—where even the oxygen cycle isn’t safe from our footprint.
Published in Science Advances, this study paints a startling picture of how human activities have reshaped the oxygen dynamics of freshwater systems since 1900. The verdict? Our lakes and rivers are gasping for air, and it’s not just a localized crisis—it’s a global one.
Oxygen: More Than Just Air to Breathe
We often take oxygen for granted. We breathe it in without a second thought. But in the natural world, oxygen is not just about respiration—it’s the silent engine behind countless chemical and biological processes. In aquatic ecosystems, oxygen fuels life beneath the surface and keeps complex food webs in motion.
Oxygen depletion in water, known as hypoxia, is already a well-documented menace. It’s the villain behind dead zones, fish die-offs, and declining water quality. But this new research shows that the issue is deeper and more complex than previously imagined. Hypoxia isn’t just happening here and there—it’s surging across the entire planet’s inland water systems. This isn’t a leak—it’s a global rupture in the balance of nature.
The Accelerated Oxygen Cycle: A Ticking Time Bomb
At the heart of this study is the first-ever global model that maps the entire oxygen cycle of inland waters. Led by geoscientists Junjie Wang and Jack Middelburg, the Utrecht team created a tool that simulates how oxygen is produced and consumed across rivers, lakes, and reservoirs worldwide.
And the results? Alarming.
The model shows that since 1900, the oxygen “turnover”—how much oxygen is produced through processes like photosynthesis and how much is used up through respiration and decomposition—has drastically increased. That means inland waters are working overtime, biologically speaking. They’re bustling with more activity than ever. But there’s a dark side to this acceleration: these systems are now consuming more oxygen than they can produce. They’re becoming net oxygen sinks, drawing oxygen out of the atmosphere instead of contributing to it.
So why is this happening?
Human Activity: The Oxygen Thief
The researchers identified two main drivers behind this change: nutrient loading and altered water flow.
- Nutrient Overload: Fertilizers rich in nitrogen and phosphorus, flushed into rivers and lakes by agriculture and wastewater, trigger explosive algae growth. It’s a phenomenon known as eutrophication. While living, algae release oxygen during photosynthesis. But when they die, their decomposition devours that oxygen in large amounts, leaving the waters depleted.
- Dams and Reservoirs: While these structures may help with water storage and electricity, they also disrupt the natural flow of water. Dams slow down the journey of water from river to sea, giving algae and other microbes more time to use up available oxygen. The stagnation also encourages stratification—layers of water that don’t mix well—making it even harder for oxygen to circulate.
Add to this mix the indirect effects of climate change, such as warming temperatures, which reduce oxygen’s solubility in water and accelerate microbial activity, and you’ve got a recipe for rapid oxygen exhaustion.
Interestingly, the study reveals a surprising twist: while global warming is often blamed for changes in aquatic oxygen, it actually plays a smaller role than direct human activities like nutrient runoff and dam building. According to Wang, warming contributes only 10–20% to the observed acceleration in oxygen cycling. That means the real driver is us—our farms, our cities, our infrastructure.
The Invisible Crisis of the Anthropocene
What makes this story even more chilling is its scale. Inland waters cover just 0.8% of Earth’s surface. Yet these small systems now remove almost 1 billion tonnes of oxygen from the atmosphere every year. That’s half of what the entire ocean emits back into the air. Think about that: our rivers and lakes—tiny slivers on the globe—are becoming black holes for atmospheric oxygen.
In the early 1900s, freshwater systems were far more balanced. They contributed modestly to the oxygen cycle and sustained aquatic life without the stress of excess nutrients or thermal pollution. But today, that balance has tipped. And the shift has been so dramatic that researchers are calling it a fingerprint of the Anthropocene.
The message is clear: we are witnessing a fundamental transformation in the way our planet breathes.
Why This Matters More Than Ever
It’s easy to assume this is just another environmental issue among many. But the oxygen dynamics of inland waters are connected to everything—from biodiversity loss and food security, to climate regulation and public health.
When freshwater ecosystems suffocate, fish populations crash. That affects not only the balance of aquatic life but also the livelihoods of millions of people who rely on fisheries. Polluted, oxygen-poor water also threatens drinking water sources, recreation, and agriculture.
Beyond that, freshwater systems are major players in the carbon and nitrogen cycles. When they’re off-balance, so are the greenhouse gas emissions they absorb or release. Disrupted oxygen cycles mean more methane and nitrous oxide—potent greenhouse gases—may be released into the atmosphere, amplifying climate change in a vicious feedback loop.
What Can Be Done?
Understanding the problem is the first step. Thanks to this new global model, scientists can now better predict where and when hypoxic conditions might arise. That opens the door to smarter interventions.
Reducing nutrient pollution is critical. That means improving wastewater treatment, managing agricultural runoff with buffer zones and eco-friendly farming practices, and restoring wetlands that naturally filter nutrients.
Rethinking dam design and placement can also help restore more natural water flows, allowing oxygen to circulate better and reducing stagnation. In some cases, removing outdated or harmful dams altogether may be the best solution.
Combating climate change is still vital—but it should be seen as part of a larger puzzle. It’s not just about warming—it’s about how all human activities interact to pressure ecosystems. Our rivers and lakes are revealing those connections in dramatic fashion.
A Final Breath
Inland waters are often overlooked in global environmental discussions. Oceans get the spotlight. Forests get the funding. But this study is a wake-up call: we can’t afford to ignore our rivers, lakes, and reservoirs anymore. They are dynamic, vital, and vulnerable.
They are not passive pools of water. They are lungs of the planet—breathing, circulating, supporting life. And right now, they are suffocating.
As we navigate this uncertain future, we must ask: Can we give these waters room to breathe again?
Reference: Junjie Wang et al, Global inland-water oxygen cycle has changed in the Anthropocene, Science Advances (2025). DOI: 10.1126/sciadv.adr1695. www.science.org/doi/10.1126/sciadv.adr1695