The French energy supplier EDF is temporarily reducing output at its nuclear power stations on the Rhône and Garonne rivers as heatwaves push up river temperatures, restricting its ability to use river water to cool the plants. The majority-state-owned company, Europe’s biggest producer of nuclear energy, said it would extend output cuts at several power stations on the two rivers as the hot spell continues – but that a minimum level of output would be maintained to keep the grid steady. EDF warned of potential output cuts at its nuclear power plants Tricastin, St Alban and Golfech in coming days due to high temperatures in the Rhône and Garonne rivers. It started imposing production restrictions in mid-July at Tricastin, St Alban and Bugey on the Rhône and Blayais at the mouth of the Garonne amid sweltering temperatures. A spokesperson told the Guardian that the company was lowering production “for a few hours” where possible but not shutting the reactors completely. After the 2003 heatwave, France’s nuclear safety authority (ASN) set temperature and river flow limits beyond which power stations must reduce their production, to ensure the water used to cool the plants will not harm wildlife when it is released back into the rivers. Temperatures in southern France are expected to reach 40C over the next two days, according to the forecaster Météo-France. Since 2000, production losses due to high river temperatures and low river flows have represented an average of 0.3% of annual production. However, half of EDF’s 56 nuclear reactors are offline due to planned maintenance and work to repair corrosion which was delayed by the pandemic, just as Europe faces an energy crunch following Russia’s invasion of Ukraine. As a result of the maintenance work, EDF estimates its power output this year will be the lowest in more than three decades. The company issued its fourth profit warning of the year last Thursday when it reported a first-half loss of €5.3bn. The French government, which owns 84% of EDF, is in the process of buying out minority shareholders to take full control of the business. The production cuts mean that France, traditionally an energy exporter, is relying on imports from countries such as Spain, Switzerland, Germany and the UK. EDF is buying electricity at high market prices, after Russia’s war in Ukraine sparked an energy crisis, leaving European countries scrambling to find alternative supplies. Another strain on EDF’s finances comes from a power tariff cap imposed by the government to shield consumers from soaring energy prices. The latest power cuts threaten to push energy prices even higher after they were sent spiralling by Russia’s invasion of Ukraine in late February.