In a plant operating 6 metal surface treatment lines (total bath volume: 196 m³), an operator observed around 8:15 pm that 1,000 liters of cyanide alkaline copper had spilled into a concrete retention basin after an output pipe detachment on a regeneration filter for the bath of a multi-treatment line.Informed of the incident at his home, the plant’s safety supervisor requested the operator to close this installation (shutdown of the heating system) and to leave the bath in the retention area. The incident was recorded in the appropriate logbook. At 5 am the next morning, at the start of his shift, an experienced operator (15 years experience in metal surface treatment) noted that the retention basin was filled with a liquid and, after referring to the logbook entry on the anomaly, decided to transfer the product with a mobile pump into the cyanide alkaline discharge tank of the detoxification station. Due to handling error, he accidentally transferred the liquid into a reservoir on the detoxification line of the chrome plating baths, which are not adapted to processing such effluent.At 9 am, the head of plant security verified, like each morning and by means of colorimetry, the pollutant concentration levels of river discharges and noted excessive cyanide content (> 2 mg/l); the shutoff valve on the sewer outfall was immediately closed. The cyanide concentration of effluent discharged into the Cher River was estimated by the operating company at 3 to 5 g/l. For the rest of the day, the detoxification station was cleaned but not entirely (specifically, the filter press was left as is), and the next day’s discharge was once again polluted with cyanide when service was restored. Between 2 and 3 tons of fish were killed by this pollution. The total quantity of released cyanide was assessed at 70 kg. The Classified Installations Inspectorate conducted an investigation, discovered the failure to respect certain guidelines of the prefecture’s operating permit (non-declaration of accidents, absence of safety instructions) and proposed that the Prefect issue a default notice.