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.