Nuclear power plants use water from rivers or the sea to cool their reactors. But in summer 2025 the weather in Europe is very hot. The water is already warm so it cannot cool the plants well. Also hot water going back to rivers can harm animals and plants.
In Switzerland the Axpo company slowed down the Beznau Nuclear Plant. One reactor stopped and the other Works at 50% power.The Aare River became 25C° which is too hot.

Switzerland wants to stop using nuclear energy by 2033 but old plants can stil work if safe.

In France the Golfech plants also stopped because the river water was too warm. Other plants like Blayais and Bugey also reduced power. But France stil has enough electricity. The company EDF says France even exports electricity to other countries.
Experts say hot weather will happen more often and energy use will go up- especially because of air conditioners.