In a food processing company’s premises housing electric generating sets, a 2,250-litre fuel oil tank overflowed into its retention basin subsequent to the malfunction of a high level alarm (due to a jammed float), triggering automatic shutdown of the supply pump. 1,000 litres of fuel oil flowed out from the retention basin, whose drain had remained open. This hydrocarbon spill polluted the CERE River over a 2-km stretch, then extended to nearly 8 km on the DORDOGNE River.