Baltic Sea ‘struggling with recovery’ and it's not just because of climate change

Euronews · Feb 23, 2026 · Collected from RSS

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The Baltic Sea has been under excruciating pressure for decades, as human activities have transformed it into one of the world’s largest “dead zones”. Due to a deadly trifecta of climate change, oxygen-sucking algae and internal matter cycles, the Baltic Sea is struggling to breathe – and years’ worth of protective measures don’t appear to be helping. A new report from the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) is now calling for tighter water management, warning that the Baltic Sea cannot recover based on a “simple cause-and-effect principle”. Why is the Baltic Sea choking? For more than half a century, the Baltic Sea has been suffering from eutrophication. This is where the environment becomes overly enriched with nutrients such as nitrogen and phosphorus, which triggers algae blooms, oxygen depletion, and the suffocation of aquatic life. When the excess algae decomposes, producing large amounts of carbon dioxide, the pH of the seawater is lowered, risking acidification. These nutrients are largely derived from human activities such as fertilisers and manure from agriculture, untreated or poorly treated sewage and industrial waste – particularly from food processing and chemical manufacturing. Nitrogen from fossil fuels can also end up in our waters, in a process called atmospheric deposition. Eutrophication often results in so-called “dead zones”, which is where there is so little oxygen that little to no life exists beneath the surface water. Through EU and national legislation, protection initiatives such as the Baltic Sea Action Plan of the Helsinki Commission for the Protection of the Baltic Sea (HELCOM) have led to a marked reduction of nutrient pollution from human sources. According to IOW, since the 1980s, phosphorus loads in rivers have plummeted by around 50 per cent, while nitrogen loads have also dropped by around 30 per cent. In 1995, total phosphorous loads into the central Baltic Sea exceeded 20,000 tonnes per year, but this dropped to around 12,400 tonnes by 2017. Despite decades of progress, scientists warn that there has been no “significant improvement” in the Baltic Sea’s surface water quality to date. Why haven’t conservation efforts helped the Baltic Sea? The Baltic Sea is a brackish, highly-stratified environment. In layman’s terms, this means it is more salty than freshwater but less salty than typical marine waters. It is also formed in layers, where less salty surface water lies above denser, saltier water. Overall, this makes it difficult for oxygen from the atmosphere to reach the deep layers. “Organic matter decomposition therefore often leads to oxygen depletion in depths, which can only temporarily be aerated by rare inflow events of salt water from the North Sea,” the report states. This rare event might be about to happen: at the beginning of February, 275 billion tonnes of water were pushed out of the Baltic Sea, lowering its level by 67 cm. The phenomenon was fuelled by strong winds, a high-pressure zone and the absence of significant atmospheric fronts. "The long-lasting strong easterly winds persisting since the beginning of January have pushed water masses through the Danish Straits towards the North Sea, resulting in a drop in levels throughout the basin," reads a post by the Institute of Oceanology of the Polish Academy of Sciences. "As long as this meteorological configuration continues, water is being 'held down' at the south-eastern end of the basins, with levels locally decreasing." When this ends, it’s expected to trigger an inflow of salty, oxygen-rich water back from the North Sea – potentially helping to revive oxygen-depleted dead zones. But the gains are unlikely to last. Is climate change to blame? While the Baltic Sea’s eutrophication is caused by nutrient pollution, climate change is undoubtedly making things worse. Surface temperatures in the central Gotland Basin have risen by an average of almost 2℃ since 1960. According to modelling in the new IOW study, a warming trend can also be observed in the deeper water layers. “Since warmer water absorbs less oxygen than cold water, summer inflows have less potential to aerate the deep Baltic Sea basins than winter inflows,” the report adds. In warmer water, oxygen is consumed more quickly, increasing the likelihood of dead zones. ‘The past has lasting effects’ Focusing on the decrease of nutrient pollution in the Baltic Sea ignores the long-term impacts of the phosphorus cycle – which is playing an important role in the ongoing eutrophication of its waters. The IOW report says that under anoxic conditions (a lack of oxygen), phosphate is released from the sediment and accumulates in the water. This is mainly due to the absence of oxidised iron compounds, which would otherwise lock nutrients in the sediment. While many are hopeful that inflow from the North Sea can help remove phosphate from the water, researchers found that in the winter of 2014, only about 30 per cent of the phosphate was removed from the water, and around five per cent was permanently buried in the sediment. “The feedback loop between oxygen depletion and phosphate release in the deep basins of the Baltic Sea also alters the phytoplankton in the surface water,” the report says. In the summer, blue-green algae blooms are less easily used in the food web. As a result, after they die off, large quantities of organic matter sink to the bottom of the Baltic Sea. “This transports phosphorous compounds into the sediment, where they continue to accumulate and stimulate oxygen depletion through the decomposition process.” This is why a drop in nutrient pollution hasn’t resulted in declining nutrient concentrations in the sea. Effectively, the Baltic Sea carries a substantial “nutrient debt” from past decades of human activity. Can the Baltic Sea ever recover? Researchers have highlighted four key management strategies to help the Baltic Sea breathe again. This includes consistently reducing nutrient pollution even further and enhancing or restoring natural coastal filters such as lagoons, fjords and estuaries, which can retain nutrients and bind them permanently. “Nature-based measures should be expanded, such as promoting seagrass beds or deliberate cultivation of microalgae to actively remove nutrients from the water,” the report adds. “Reefs and mussel beds also contribute to this.” The report also calls for “long-term observation and modern measuring systems” to be expanded, arguing that new sensor systems will help detect improvements and setbacks at an early stage.