Heavy fuel oil, originating from a chemical plant and used as fuel for a glass furnace, polluted the River SAONE. The alert was raised at 6 am by the patrol team. The operator rapidly implemented its pollution containment procedure by installing booms at the outlet of the plant’s aqueous effluent discharge pipe. This system was replaced by a 45 m floating boom one and a half hours later when the fire-fighters arrived. Most of the pollution was contained in the waste water treatment plant of the factory and was cleaned by being pumped out by a specialist company. The hydrocarbons retained by the floating boom were also pumped out. A few 1 to 2 m² pollution stains drifted down the River SAONE and apart from the sheen and the presence of visible oily patches on the river, oily residues on the rocks and flora were the only signs of pollution close to the discharge site. The area was cleaned up on the same day. The hydrocarbon leak originated from the installations transporting the heavy fuel oil to the melting furnace but its cause was not clearly established. The 2 to 3 m³ tank placed under the pump unit most probably overflowed, as a 4 m² puddle was visible below it. Given the viscosity of the product, the product slowly flowed into the industrial water network. The operator must carry out an investigation to determine the causes of the accident and take the necessary steps to prevent a recurrence. It will need to characterise the extent of the pollution and decontaminate the polluted area. Investigations will also be carried out to identify the possible consequences of the fuel oil spillage on soils.