An outbreak of hydrocarbon pollution occurred in a port basin after an incident at a fuel storage site (holding fishing boat diesel) operated by a maritime cooperative. When closing the site at the end of the day Saturday, the employee assigned to shut down installations turned off power to the pump/centrifuge used to transfer diesel between 2 tanks but forgot to close 2 of the 3 isolation valves, namely those on the pump tanks. Diesel from one of these above-ground tanks flowed by gravity into the pump filtration system connected to a hydrocarbon separator. Once the various compartments of this separator had become saturated, diesel flowed via the outlet leading to the storm drain network and emptied directly into the port. This spill was detected the next morning by a passer-by, who notified emergency services. Given the windy conditions, the pooling diesel was confined to a corner of the basin, which allowed for quick confinement by a floating boom set up by first responders, who recovered the diesel by pumping as well as using absorbent water repellents. The quantity lost was estimated at 20 m³, of which 8 m³ were collected on-site. The total quantity of waste recovered on-site and in the port was approx. 33 tonnes, broken down as follows: 31 tonnes in liquid form and 1.9 tonnes as solids. Subsequent to this incident, the port operator installed a solenoid valve servo-controlled to centrifuge operations to close the diesel intake upon centrifuge shutdown. Also installed was a liquid presence detector on the pumping station floor, connected round the clock to a remote monitoring control room, along with a detector of the same type around the hydrocarbon separator outlet, with the same remote monitoring connection.