Warming continues across all basins of Lake Balaton, with surface temperatures peaking at 32.9°C near Keszthely on Monday, according to monitoring data. For now, no significant algal bloom has been observed, the Balaton Limnological Research Institute reported on its Facebook page on Tuesday.
Water temperatures reach extraordinary levels
Researchers in Tihany, citing data from hydrological monitoring platforms, said the warm surface layer is now penetrating noticeably deeper into the water column than it did last week. Average surface temperatures recorded on Monday afternoon stood at 32.3°C in Keszthely, 32.1°C in Szigliget, 31.8°C in Balatonszemes and 31.7°C in Siófok.
Peak readings were registered within the upper five centimetres of the water column near Keszthely. In practical terms, this corresponds to the sort of temperature one might expect from a pleasantly warm bath; increasingly, however, it is less suited to swimming and offers little in the way of refreshment.
At Szigliget, pronounced thermal stratification has developed. A distinctly warm layer now extends from the surface down to a depth of around one metre, sitting above a comparatively cooler layer below roughly one and a half metres. Researchers stressed that in nearshore zones and at beach entry points, water temperatures may be considerably higher still on both the northern and southern shores.
No immediate sign of algal bloom
For the time being, there is no evidence of heightened algal growth. However, the unusually high temperatures affecting both the water column and sediment, together with the emerging stratification, are likely to play a decisive role in shaping water quality and the lake’s ecological functioning in the weeks ahead, the Tihany institute warned.
Measurements taken by an instrument positioned off the Siófok meteorological observatory recorded temperatures of up to 29.5°C at a depth of one metre on Monday, according to the observatory’s head, Ákos Horváth.
A prolonged heat event is not yet certain: a cold front accompanied by severe storms is expected to arrive as early as tomorrow.
Why elevated water temperatures matter
Higher water temperatures favour the proliferation of cyanobacteria — commonly known as blue-green algae — which can trigger algal blooms, degrade water quality and pose potential health risks. Oxygen levels in the water may also decline, threatening fish stocks and disrupting the lake’s delicate ecological balance.
Experts warn that sustained warming could, over the longer term, significantly affect both the biodiversity of Lake Balaton and its appeal as a tourist destination.
Lake Balaton is under siege from multiple threats
Lake Balaton is under siege from multiple threats, the head of the Balaton Limnological Institute, Gábor Vasas, said, referring to building new developments on the shoreline, dying reed beds, pollution from sunscreens, chemicals, and pharmaceuticals, as well as warming waters driven by climate change, the Hungarian News Agency wrote.
The public often fixates on water levels, Vasas said on the Hungarian Academy of Sciences’ (MTA) Biztos Hang podcast, but the lake’s health depends on natural fluctuation, not a static ideal. A range of 70 to 110 centimetres is normal for a shallow lake, while prolonged high or low levels can both cause ecological harm.
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A bigger concern is the lake’s water balance, he said. Since 2000, years with a negative balance — where more water is lost than replenished — have become more frequent. Climate change is intensifying droughts, and shallow lakes like Balaton are especially vulnerable to shifts in temperature and precipitation, he added.
Reed beds, critical for habitats, fish reproduction, and water filtration, cannot simply be replanted elsewhere if destroyed for building developments. Their loss threatens the lake’s functionality, not just its scenery, he stressed.
New risks are emerging, Vasas warned, noting that warming waters can trigger internal nutrient release from sediments, causing algae blooms even if external pollution is reduced. Everyday use of sunscreens, chemicals, and fishing feed also adds to the burden, while invasive species pose growing threats due to climate change and human activity. The lake’s future hinges on finding systemic solutions, Vasas said.
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