Around 2:30 pm, municipal employees noticed a blue colouration of the INDRE River over a 400 sq. m stretch. The facility responsible for the pollution outbreak was quickly identified. At 3:20 pm, management stopped all activity at the faulty plant (floc production) and rerouted its discharges, which were normally channelled into the municipal wastewater network for treatment at the city’s treatment plant, at a water retention basin. Despite the dyes and discharge temperature (60°C) associated with this pollution, no dead fish were observed. The discharge volume of industrial water associated with the day’s operations amounted to 6,000 litres; no information however made it possible to quantify the actual proportion of this volume emptying into the INDRE through the site’s storm drains. After investigating the plant’s water systems, a wastewater network cleaning job indicated no clogging. The pumping of residual coloured water revealed a blinding plate in one of the network’s manholes. This plate contained a 15 x 5 cm hole providing access to a pipe not shown on the lone sketch of the site’s water systems; this pipe connected the site’s wastewater network to the rainwater drain pipe of the neighbouring business. A plugging balloon was inflated to block and seal the connector pipe running between these 2 networks. A test conducted around 6 pm verified the absence of any discharge, and the plant resumed operations 30 mins later. The age of these water networks, their complexity and a lack of familiarity with these systems combined to cause this accident. The site’s only known water network drawing was actually incomplete. After noting observations, it appeared that works had been performed to separate the site’s networks (clogged, blocked pipelines). An as-built water network drawing for the site along with network compliance upgrades were necessary. These water networks could be separated by definitively shutting connections and not by using metal plates or valves. Regular monitoring (every 3 hours) of the temporary plugging system to ensure network separation was requested until permanent repairs could be organised. The site operator was also required to submit an accident report with proposed corrective actions.