Captain André Machado, of the GNR's Portalegre Territorial Command, explained to Lusa that the situation was reported by the public on 28 March, with the polluting discharge having been made in Ribeira de Nisa, in the parish of the same name, in the municipality of Portalegre.
"The situation was denounced around 2pm. The water presented, at the time, a stain with a whitish tint, did not cause foam, had no odour," he reported.
The officer also explained that, in the meantime, the stain "disappeared completely", leaving "no marks or any kind of residue" in the water course.
Captain André Machado also mentioned that the public reported to the authorities that, "sometimes", at weekends, the water usually becomes "slightly more turbid".
GNR is developing a set of diligences to investigate this case, namely to ascertain the origin of the polluting discharge.