High temperatures registered in the Rhone and Rhine rivers, from which the three power plants pump their water for cooling, led to a temporary shutdown of the reactors.
Two of the halted reactors belong to EDF's Bugey plant, one is located at St. Alban and one in Fessenheim near the German border.
France, like much of Europe, is experiencing scorching weather in its southern regions, with forecasts showing temperatures reaching 37 degrees Celsius (98.6°F) in the Rhone valley.
Temperatures were near record highs on Friday in Spain and Portugal and will remain above 40 degrees Celsius at least until Sunday.
EDF's nuclear plants along the Rhone and the Rhine use the rivers' waters to regulate the temperature of their reactors, discharging warm water back into the waterway.
Curbs are placed on the volume of water its plants can use as the river temperature rises.
