A frozen lake in Czechia recently turned a striking green, signaling notable ecological shifts from climate change. Researchers at the Biology Center of the Czech Academy of Sciences discovered that a bloom of toxic blue-green algae, known as cyanobacteria, was responsible for this unusual color change in Lake Lipno during December 2025.
Typically, cyanobacteria blooms thrive in warm weather during summer and autumn, but this year, they lingered into winter. The algae turned patches of ice green by absorbing sunlight, which was enhanced by calm weather and a few weeks of sunshine, as detailed by the researchers in a recent study.
Lake Lipno, the largest reservoir in Czechia, struggles with nutrient overload from industrial waste, agricultural runoff, and other human activities. These pollutants are a primary cause of cyanobacteria blooms that can poison aquatic life and pose health risks to people.
In the past, these blooms would vanish by the colder months. However, recent findings show they now sometimes hang on until winter, creating what researchers referred to as “cyanobacterial eyes.” These are clear patches of ice that form above the algae, making them visible underneath.
The phenomenon peaked around Christmas, with warmer temperatures briefly melting the ice before it refroze, allowing distinct cyanobacterial eyes to emerge. Interestingly, researchers predict that this eerie green ice could become a more common sight in the future as climate change progresses.
Petr Znachor, a hydrobiologist involved in the study, highlighted that these occurrences reflect long-term changes in our environment. “Green ice on Lake Lipno fits into the long-term trends we observe here in connection with eutrophication and climate change,” he noted. “Expect more surprises like this as our climate continues to shift.”
Echoing this sentiment, a 2022 report from the European Environment Agency found that extreme weather events linked to climate change are increasing across Europe, including more frequent algae blooms. As communities grapple with these changes, the phenomenon on Lake Lipno serves as a striking reminder of how our ecology is shifting.
Climate impacts like these are not just isolated to Czechia. Similar patterns are seen in lakes around the globe, suggesting a widespread issue that demands our attention.
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Bacteria,Climate change,snow
