Switzerland’s drought exposes uncertainty over its water reserves

Lake Zurich has crossed a line Switzerland has not seen in 75 years. On August 19, its surface fell to 404.45 metres above sea level—below the previous record of 405.46 metres set in 1952. The plunge delivers a stark visual warning after months of heatwaves and scarce rain have pushed the country into what the Federal Office for the Environment calls a “marked drought”.

The crisis reaches far beyond Zurich’s shoreline. Federal officials report dry soils and depressed surface and groundwater levels, with Lake Constance and Lake Maggiore also running below seasonal norms. Lake Zurich Ferry has already restricted heavy vehicles on the Horgen–Meilen crossing because the “extraordinarily low” water level is limiting operations.

Yet Switzerland’s drought story is not uniform. Lake Geneva remains near its annual average, helped by rivers swollen by glacier melt. That contrast is the central mystery now confronting water managers: some reservoirs are visibly shrinking, while others appear resilient. The country knows the water on its surface is under pressure. It knows far less about how long the reserves beneath its feet can withstand the next dry spell.

The most important water reserve in Switzerland is also the least understood. More than 80% of the country’s drinking water comes from larger underground sources—aquifers that store water from winter and spring and release it gradually. They can look healthy long after shallow sources have begun to fail. That apparent strength, however, can conceal a dangerous information gap.

Researchers working in canton Fribourg are building models to determine how individual springs respond when rainfall disappears and temperatures climb. The task is urgent because groundwater is unevenly distributed, and existing monitoring does not provide a detailed national picture. Officials cannot yet say with confidence which sources are approaching trouble, or how quickly they might recover.

The problem is not simply a lack of measurements. Researchers need to know a spring’s total output, not merely how much water reaches a reservoir. That distinction can determine whether a source is genuinely stable or only appearing stable because extraction and natural flow are being measured incompletely.

Switzerland’s reputation as a water-rich country rests on reserves that are largely hidden. Climate change is now forcing authorities to measure the foundation of that security before another drought tests it harder.

A spring in Fribourg is still flowing at 1,100 litres a minute—but a stream nearby has already vanished. The two sources sit close enough to expose the complexity of Switzerland’s water crisis. The spring’s output is slightly below its long-term July average, yet hydrogeologist Julie Boillat describes it as “kind of normal for July”. On the national drought map, the area remains green.

The nearby stream tells a harsher story. It has run dry, prompting Guillaume Balmat, who oversees the village water supply, to call it a “visual witness” to declining water production in the catchment. The difference reflects how water moves underground. Small, shallow groundwater systems and sources fed by local streams react quickly when rain fails. Larger aquifers, replenished during winter and spring, can buffer the shock for much longer.

That resilience is real—but it is not infinite. The spring’s current flow reflects water that fell as rain or snow in February, meaning today’s reassurance may depend on months-old conditions. As droughts become more frequent or prolonged, those deep reserves could face pressure with little visible warning. The challenge is to identify that turning point before taps, farms and ecosystems feel it.

Switzerland is beginning a race to measure the water it has not been watching closely enough. Canton Fribourg currently has six groundwater sensors, and four have collected more than a year of data. Two show water levels roughly one metre lower than last summer, but researchers insist the record is still too short to support firm conclusions.

The federal monitoring network cannot fill the gap. It covers only two springs across the entire canton—enough for a broad impression, not a detailed map of local risk. Fribourg plans to install 30 additional sensors this year, while researchers develop models capable of tracking a source’s full output and drought resilience.

The work may sound technical, but its consequences are immediate. Without reliable data, cantonal authorities cannot easily distinguish a temporary dip from a structural decline. That uncertainty complicates decisions about drinking-water protection, agricultural withdrawals and emergency planning. It also makes it harder to compare conditions between regions, even as lakes and springs respond in sharply different ways.

Switzerland now needs more than a national drought map coloured in green, yellow or red. It needs a living picture of underground reserves—one detailed enough to show where the next crisis is forming before the surface reveals it.

The drought is redrawing Switzerland’s water map—and forcing decisions across borders. Lake Maggiore’s critical level triggered an emergency meeting by the Italian-Swiss body responsible for regulating the lake. Authorities then allowed a larger outflow from Lake Lugano, amid fears for rice-growing districts downstream in Novara, Lomellina and the Milan area.

Meanwhile, Lake Geneva remains close to its annual average at about 372 metres above sea level, benefiting from river inflows strengthened by glacier melt. The contrast with Lake Zurich’s record low is dramatic: one major lake receives a temporary boost from a warming Alpine system, while another exposes the consequences of months of deficient rainfall.

That unevenness makes simple national conclusions dangerous. Switzerland may still possess substantial underground reserves, but their protection and replenishment vary from canton to canton. Surface-water shortages can disrupt ferries, farming and ecosystems before authorities understand what is happening below ground. Cross-border lakes add another layer, requiring rapid coordination with Italy, Germany and Austria when levels fall.

The immediate question is not whether Switzerland has water. It is whether the country can locate, measure and manage enough of it as climate pressure intensifies. The answer will shape how Swiss communities plan for every dry summer ahead.