The RUAU river was polluted by 150 l of latex (styrene butadiene in emulsion at 50%) that had overflowed from a 29 m³ tank at the end of the unloading of a 24 m³ road tanker in a paper mill. The watercourse has a milky white colour. Technicians cleaned the outside of the tank and the equipment with 500 l of water. The 650 l of latex diluted to 12% present in the retention area of the tank were pumped and stored in a container, but the cause of pollution remained unidentified. At around 3 pm when pumping had finished, it was noted that the watercourse had changed colour again; approximately 100 l of effluents had escaped from the bottom of the retention area through a PCV pipe and had entered the rainwater network. The VAIR river, located 100 m downstream, was polluted in turn at around 5 pm. Three main elements contributed to the accident: the tank had been too full (it already contained 4 m³ of product before the unloading); the inlet pipe did not reach the bottom of the tank, which had facilitated the foaming of the product; the concrete used to isolate the PCV pipe from the bottom of the retention tank was not leaktight. Following the accident, the operator revised the pipe closing system and cleaned the rainwater network. The type of unloading causing the spillage was carried out once only before the accident, as latex had been used beforehand premixed with a talc suspension.