Lake Balaton in danger: Unusual phenomenon observed, swimming not recommended – PHOTOS, VIDEO
Despite an unusually cool spring, large quantities of algae have recently appeared in Hungary’s largest lake, Balaton, surprising researchers and raising concerns about the long-term impacts of climate change and water quality.
Green waters from north to south
Visitors and weather observers began reporting greenish water at multiple locations along Lake Balaton’s shoreline over the weekend, Időkép reports. The phenomenon was especially noticeable near Balatonszepezd on the northern shore and Balatonboglár on the southern side. According to Időkép, even at a distance of 50 meters from the shore, the greenish hue of the water was clearly visible.
While algal blooms are not new to the Hungarian sea, what makes this episode unusual is the timing. Previous algal outbreaks typically followed extended periods of hot weather. This time, however, the bloom emerged after a particularly chilly May, without any prolonged heatwaves.
What’s behind the bloom?
As Telex writes, according to Dr. Gábor Vasas, acting director of the HUN-REN Balaton Limnological Research Institute, the sudden appearance of algae is linked to a brief spike in temperatures following the cool spring. Warm weather and increased sunlight helped trigger the early summer bloom of Dolichospermum spiroides, a type of cyanobacteria (commonly referred to as blue-green algae), which became concentrated near the shorelines due to light winds.
Routine monitoring by the institute showed that the average chlorophyll-a concentration (a measure of algal biomass) remains well below the World Health Organisation’s safe threshold of 75 µg/l, currently hovering between 8–10 µg/l. However, local spikes occurred in shallower bays, especially in the lake’s western basin, where conditions favoured algae growth.
Although researchers are still awaiting lab results to determine the potential risks of the current bloom, Dr. Vasas advised swimmers to be cautious. In areas where dense, green, almost creamy algae masses are present, people (especially those with sensitive skin) may experience rashes. Accidentally ingesting the water could also lead to stomach issues such as diarrhoea.
Climate change as the underlying driver
Experts point to long-term climate change as a key factor behind the increasingly frequent algal blooms in Balaton. A recent study published on the Másfélfok science platform highlights how the lake’s average water temperature has risen by approximately 1.7°C since the year 2000. This warming trend, three times faster than during the previous century, has been particularly intense during winter months.
The rise in temperature is disrupting the lake’s seasonal biological rhythms and increasing the risk of oxygen-depleted periods. Combined with dropping water levels and nutrient enrichment (due to runoff from agriculture and urban development), these conditions create an ideal environment for algae to thrive.
A changing ecosystem
Not only are algae more prevalent, but the warmer waters are also altering the plant life in the lake. Invasive, heat-tolerant aquatic plant species, including the spiny Najas guadalupensis and rough Ceratophyllum demersum, are outcompeting native flora. Scientists warn that the future may see more Mediterranean and even tropical plant species entering Balaton’s ecosystem, fundamentally transforming the lake’s biodiversity and possibly diminishing its appeal as a recreational destination.
What can be done?
While short-term solutions remain limited, experts emphasise the importance of monitoring, sustainable water management, and action to curb climate change. For now, visitors to Lake Balaton are advised to avoid swimming in visibly green or algae-dense areas and to shower after bathing in the lake.
Check out more photos of the water in Időkép’s article.
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