Between 5:30 and 10:00 am, several pollution episodes were observed at the level of a lock and over a strip 500 m long by 10 m wide at the RHONE River surface. One of the pollutants seemed to be organic in nature, as well as immiscible, slightly oily and featuring a bluish iridescence. Other substances of a whitish colour (sticky resin) were also present. No visible impact on the local aquatic fauna could be detected and a downstream warning post also found no pollution surge. A collector pipe shared among 3 chemical plants was quickly identified as the origin of this discharge. The Inspectorate specialised in hazardous installations extracted a number of water samples, and a particularly odorous one contained a high concentration of xylene (145 mg/l – as opposed to an imposed value of 4 mg/l). An investigation was requested at the level of all three of the suspected sites. One of them, which manufactures silicone products, was found to have caused the pollution: solvent overflow on a xylene distillation and resin concentration line had occurred subsequent to an inoperable control valve on a heating circuit. An inappropriate configuration involving retention ditches and sewers near site building works led to a direct discharge of 200-400 kg of xylene into the natural environment. Installations were shut down and work got underway to reduce the probability that this type of accident repeats.