At 4 pm, textile mill employees noticed a leak on a 30-m³ fuel oil tank located within a retention basin; they drained the tank at night and clogged the leak. On 7th June, fire-fighters observed an iridescence on the LYS River over a 10-km stretch 1.50 metres wide. They spread dispersant and absorbent, then proceeded the next day by erecting a 12-m water-repellent barrier. A plant 3 km downstream was no longer able to pump river water to meet its industrial needs and was operating on a 48-hour drinking water reserve. Both the municipality and classified facilities inspectorate were duly informed.

The retention basin displayed several cracks. The fuel oil remaining in the basin would have spilled via older pipes that did not appear on the drawings and emptied into the LYS River 5 m away. Responders tried to stop the leak with a Vetter cushion, but the plugging effect was only partial due to the installation’s poor state of repair. A specialised subcontractor scoured the retention basin.

The classified facilities inspectorate requested the operator to submit an accident report and refrain from restarting the tank before first diagnosing its condition and performing the appropriate repairs. An emergency order was proposed to the Prefect.