Beznau nuclear power plant reduces output due to high Aare water temperatures

The Aare reached 25 °C yesterday. Axpo has therefore been increasingly reducing the output of both units of the Beznau nuclear power plant for several days and yesterday reduced it to 50 %. This measure serves to protect the Aare ecosystem and to comply with all environmental regulations.

The ongoing high temperatures in Switzerland have led to the Aare River below the Beznau Nuclear Power Plant reaching a water temperature of 25 degrees Celsius on 29 June 2025. In accordance with the provisional ruling issued by the Swiss Federal Office of Energy (SFOE), Axpo has reduced the output of both reactor units to approximately 50 percent. This output reduction was initiated several days ago and has been gradually intensified as water temperatures continued to rise. The decisive factor is the temperature of the Aare River downstream of the Beznau site. 

This measure is aimed at protecting the Aare’s ecosystem and complying with strict environmental regulations. The cooling water for the Beznau Nuclear Power Plant is drawn from the Aare and returned to the river after use. During hot summer periods, it is essential to prevent any further heating of the already warm river water in order to avoid additional stress on aquatic flora and fauna. 

"We are fully implementing the requirements set by the authorities. The reduction in reactor output is a prescribed measure to protect the ecological balance of the Aare River," says Michael Kessler, Head of the Nuclear Energy Division at Axpo.  

Security of Supply Remains Ensured

Even at reduced output, the Beznau Nuclear Power Plant continues to contribute to Switzerland’s electricity supply. Axpo is in close contact with the relevant supervisory authorities and is continuously monitoring the water temperature levels. Should weather conditions worsen further, Axpo is technically and operationally prepared to safely and systematically shut down both units if necessary. 

Transparency and Responsibility

Axpo is committed to sustainable energy production in harmony with people and nature – even under challenging climatic conditions. The public is informed proactively about relevant operational developments.