(Bloomberg) -- Electricite de France SA will probably have to reduce nuclear output over the coming weekend as a heat wave affecting a large part of the country warms rivers used for cooling some of its reactors. 

Due to the high temperatures forecast on Rhone river, production restrictions are likely to affect production at its Tricastin power plant — where two of its four 900-megawatt reactors are already offline for maintenance — on Aug. 26, EDF said in a regulatory notice Monday. Output at EDF’s Bugey facility may also be reduced Aug. 26 and 27, the utility said.

France’s fleet of 56 reactors provide more than half of the country’s power and are a cornerstone for Europe’s electricity market. While the potential reductions are no cause for concerns in terms of energy supply at the weekend, they could support market prices in coming days if it means France’s exports to neighboring countries is curbed.  

Read more: Heat Still Stifles Parts of Europe as Fires Burn in Greece

The river water in these areas isn’t too hot to be used for cooling, but could rise to levels that threaten wildlife if the reactors continue normal operations in the unusually warm weather. For this reason, the levels to which these plants are allowed to increase river temperatures are strictly monitored and controlled.

On Monday, EDF extended its warning that output of the Golfech plant in southwestern France might be affected until Aug. 29 due to high temperatures in the Garonne river. 

Read more: French Nuclear Reactor Availability Drops to 61% 

--With assistance from Todd Gillespie.

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