France's hydroelectric stocks fell by one percentage point last week to 51% of capacity, putting them equal with levels recorded this time last year, the latest data from grid operator RTE showed Tuesday.
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High levels of rainfall this winter boosted supplies but heavy usage of hydroelectric plants has dented stocks in recent months.
At the start of March, hydroelectric supplies were 19 percentage points above reserves at the same time in 2013.
French nuclear power output fell in the first quarter of this year and hydroelectric plants were heavily used, despite lower power demand on milder weather.
Dominant power generator EDF controls France's 58-reactor nuclear fleet and most of the nation's hydroelectric capacity.
Quarterly output from EDF's nuclear power plants fell by 0.8% year on year to around 114.5 TWh, an analysis of RTE data shows.
French hydroelectric output in the first quarter of 2014 climbed by 8.9% to around 19.8 TWh as hydroelectric plants were largely favored over fossil fuel output.
France's hydroelectric reserves usually start to pick up around this time of year, boosted by springtime rainfall and mountain snowmelt in what is typically a low demand period.