With heat waves bringing temperatures into the upper 90s Fahrenheit this summer, a swim in the Rhine River has been one of the best ways to cool off in Basel, Switzerland. But all the heat in the air, combined with a weeks-long drought, has made a dip a little less refreshing.

“It is crazy in comparison to past years that it’s so warm already,” said Lisette Reideger, a regular Rhine swimmer. “It does not really feel right.”

The Rhine was several degrees warmer than usual this summer, and Reideger said she was able to start this year’s swimming season earlier than usual since the water turned warmer sooner.

As the temperature climbed, water levels fell because of this summer’s drought and reduced snowpack in the mountains last winter, which meant less cool meltwater flowed downstream.

On one recent day in July, a few swimmers passed by as Reideger noted that the river’s flow was slower than usual, with a relaxing float through the city now taking much longer.

But while the people moved slowly, boats didn’t move at all. Freight shipping on Europe’s rivers has been disrupted by drought, causing logistical headaches for major industries. River cruise operator Viking reports that half of its European cruises have been affected by low water levels, leading to parts of the trip being done by bus or to passengers switching boats. In Basel, one of the city’s iconic ferry boats that shuttle passengers across the Rhine briefly suspended service due to low water levels. 

Beyond rivers, lakes have also begun to shrink and heat up. Some lakes reached near-record temperatures as early as May.

“These conditions can be lethal, basically. We actually get records of fish dying,” said Christoph Vorburger, a professor at the Swiss Federal Institute of Aquatic Science and Technology.

Warmer water doesn’t dissolve as much oxygen as colder water. This means the trout, salmon and other native fish can’t breathe. If temperatures stay this way, new species will settle in.

“One of the big beneficiaries that is becoming more and more abundant, especially in the large rivers and lakes, is the catfish,” Vorburger explained.

Warmer, stagnant water can be more susceptible to algae blooms, as well, which can be a hazard for swimmers or for pets that may drink the water. And they can make for eyesores for the many tourists who make a lake trip part of their vacation.

Images of dry riverbeds and abnormally low lakes have been plastered across newspapers and televisions this summer. Vorburger said it’s unlikely any rivers or lakes will dry up completely or permanently, but more dry summers like this will make water management a bigger concern going forward.

“I think these low water levels in streams and rivers will become more frequent, and I also think patches drying up will unfortunately become more frequent,” he added.

Heat also increases energy demand for fans and, increasingly, air conditioning. Here, warm water works against the power infrastructure. 

Most of Switzerland’s electricity comes from hydropower, with nuclear making up most of the remaining share. Warm water makes hydropower less efficient. Nuclear reactors also need cool water to keep cool. This summer, the Beznau nuclear plant was shut down when the water in the Aare River got too warm.

Fortunately, hot months are better for solar production, which will have to be ramped up to avoid burning fossil fuels to make up electricity gaps, something that would make a vicious cycle even worse.

“We are in a different climate regime, so we have to adjust to those conditions. But if we don’t stop emissions, we basically have to keep adapting to moving targets,” said Sonia Seneviratne, a professor for land climate dynamics at the federal institute of technology in Zurich.

Steady rainfall and a snowy winter could bring water levels and temperatures back to historical norms. But even if emissions drop, carbon dioxide will stay in the air, Seneviratne said. So, this cycle of heat and drought may now just be the new normal.