Scientists say the economic cost of the river’s demise is only part of the problem. Gabriel Singer, an ecologist at the University of Innsbruck in Austria, explains that the less water there is in the entire water system, the less salt is diluted and the slower the river flows. This results in higher salinity and higher water temperatures, which can be lethal for many species of river life, such as Danube salmon, Babel and European grayling.
Higher temperatures also breed algae, which can be toxic to river systems, Singh explained. That’s what happened in several German rivers, including the Moselle and Neckar, and perhaps the Oder, where in mid-August there were over 100 metric tons (220,000 pounds) of dead fish — including bass , catfish, barracuda, and asp – washed up on its shores within a week. (Experts are currently investigating the cause of death.)
Scientists point out that while the plight of Europe’s big rivers has made headlines, it is the smaller rivers that suffer disproportionately. “Many of them were completely dry, not a drop of water was left,” Link said. “When that happens, they lose their entire biodiversity community forever. The next time it rains it won’t come back.”
Thousands of years of engineering and human activity along European rivers also played a role, scientists say. Straightening of once wild rivers, deforestation, damming, industrial pollution, wastewater discharge and agricultural encroachment on coastlines and wetlands have made Europe’s rivers more vulnerable to heatwaves and low-water conditions, as well as flooding.
“All of our river systems are highly fragmented and vulnerable,” Singer said, stressing that while the lower Danube is plagued by drought, the upper Danube in Germany and Austria could be at risk of flooding, as happened on the Rhine last July as spectacular as the German-Belgian border. The underlying problem, he says, is basically the same: Highly remodeled rivers and watersheds cannot hold water for long. “A healthy natural ecosystem is like a sponge, providing and absorbing water, but we’ve lost that ability,” he said.
“We lose a lot of water because rain cannot penetrate sealed surfaces, and heavy rain after a drought cannot penetrate dry soil,” explains limnologist Christian Gribler of the University of Vienna. and fast-flowing rivers that almost communicate with the surrounding aquifers.”
As a result, Singer and Griebler say the authorities’ reflexive response — digging deeper — doesn’t address the underlying problem. In fact, it exacerbates it.
Addressing the crisis unfolding along Europe’s rivers this summer will of course require a long-term effort to slow global warming. In the short term, governments need to address other factors that are putting pressure on the continent’s waterways, including strengthening protection of wetlands, scientists say.
On this front, Singer said, some progress is being made. Last year, UNESCO established the world’s first five-nation biosphere reserve—almost 1 million hectares (3,860 square miles)—along the Mura, Drava and Danube rivers.
The Danube Delta, Europe’s largest wetland, has enjoyed this protection since 1998. But the delta’s special status doesn’t make it immune to extreme weather. Freshwater springs in Delta Letia Forest dry up in August, endangering the lives of Romania’s famous wild horses. Officials used bulldozers to level the silt springs so the water could flow again and the horses could drink.
“Fortunately, during times of lower precipitation, we still have glaciers that serve as reserves for larger rivers,” Hein said. “But climate change modelers say they’re going to be gone in 30 years. That’s very concerning.”
Adaptation measures must ultimately be part of the basin’s future, said Robert Lichtner, the EU’s strategy for the Danube region in Vienna. “We want to slow down these processes, but extreme weather is not going away,” he said. “We have to adapt and learn to live with it.”
