In a statement released on Friday evening (6 October), the Helsinki-headquartered forestry and biomaterials giant said that on 16 August 2023, it was notified of an alkaline leak in the storage area at the mill, which had led to abnormal water colour and fish mortalities in a creek that runs through the mill site and the bordering field.

The leak was caused by defects in the stormwater control basin of the chemical storage and unloading area of the mill, UPM said.

The leak led to the presence of sodium hydroxide and therefore high pH values in the water of the creek.

The water quality was also affected in the zone in which the creek runs into the Río Negro river, but to a lesser extent.

“UPM immediately took the applicable corrective measures to address the situation and prevent any further leakage,” the business stated.

“We informed the environmental authorities and the mill neighbours of the incident and published an announcement on the UPM Uruguay website.

“The pH value of the affected watercourses returned to normal levels within a few days. UPM and the Uruguayan environmental authority DINACEA have investigated the causes and consequences of the incident, and UPM will implement all the necessary actions, including monitoring, as instructed by the authorities. We have also taken all measures to prevent similar incidents in the future.

“UPM expects to receive monetary sanctions imposed by the authorities in line with Uruguayan legislation.”

The company added: “UPM strongly regrets this incident and takes it very seriously. Our environmental management processes, controls and monitoring worldwide are rigorous, and this type of incidents are very rare in our operations.”

The new Paso de los Toros mill started up in April this year and was set to increase the group’s pulp capacity by more than 50%. The greenfield mill involved an investment of $3.47bn (£2.85bn).