Lakes around the world are rapidly losing oxygen, a trend that scientists warn could have devastating consequences for aquatic life, global food security, and climate stability. A new study published in Science Advances on March 21, 2025, has revealed that deoxygenation in global lakes is occurring at a rate faster than that observed in oceans and rivers.
The research led by Yibo Zhan of the Chinese Academy of Sciences, found that 83 percent of the 15,535 lakes studied are experiencing continuous oxygen loss, with the decline driven primarily by rising global temperatures and an increasing frequency of heat waves.
The study identified long-term climate warming as the primary driver of oxygen loss, accounting for 55 percent of the depletion in surface waters. As temperatures rise, the solubility of oxygen in water decreases, leading to lower concentrations in lakes. Eutrophication, caused by excess nutrients from pollution and agricultural runoff, contributes to an additional 10 percent of the decline.
Projections suggest that surface dissolved oxygen levels will fall by 0.34 mg/L under the SSP2-4.5 emissions scenario and by 0.76 mg/L under the SSP5-8.5 scenario by the end of the century. North America and Europe are expected to experience the most severe impacts due to a combination of rising temperatures and more frequent heat waves.
The study highlights that tropical lakes will be among the hardest hit, with hundreds of water bodies expected to face severe oxygen stress by 2100. Under the SSP2-4.5 scenario, 238 lakes are projected to reach critical low-oxygen conditions, while under the more extreme SSP5-8.5 scenario, the number rises to 279. One of the most alarming cases is Lake Victoria, Africa’s largest lake by area, which is expected to suffer prolonged periods of low oxygen, threatening its biodiversity and the millions of people who rely on its fish stocks for their livelihoods.
Using ERA5 reanalysis data from 2003 to 2023, the researchers also found that heat waves over global lakes have become increasingly frequent, averaging 15 days per year. The number of heat wave days has been rising across all six continents, with Africa seeing an increase of 1.2 days per year, Asia 0.7 days, Europe 0.6 days, North America 0.5 days, Oceania 1.4 days, and South America 0.6 days. These extreme heat events further accelerate deoxygenation by reducing oxygen solubility and causing abrupt fluctuations in dissolved oxygen levels.
The consequences of declining oxygen levels in lakes are far-reaching. Aquatic species that depend on well-oxygenated waters may face habitat loss and potential extinction. A reduction in oxygen availability also limits nitrogen fixation, which is essential for aquatic ecosystems, while increasing emissions of nitrous oxide, a potent greenhouse gas that contributes to climate change. The loss of oxygen could lead to mass fish deaths, jeopardizing commercial fishing industries and threatening the food security of millions who rely on freshwater fish as a dietary staple.
Scientists warn that if deoxygenation continues unchecked, lakes could become ecological dead zones, unable to support aquatic life. Zhang Yunlin, a co-author of the study, emphasized the urgency of addressing this crisis, stating that the continued decline in oxygen levels could lead to species extinctions and the collapse of entire ecosystems. With lakes playing a crucial role in supporting biodiversity, regulating climate, and sustaining human livelihoods, researchers are calling for immediate action to curb greenhouse gas emissions and implement stronger conservation measures to prevent irreversible damage.