The waters of the Mätäjoki River in Helsinki's Tali neighbourhood began smelling strongly of turpentine on Monday afternoon and local residents found fish floating belly-up in the stream.
According to Helsinki Emergency Services, the source of the chemical discharge is likely to be an industrial facility in the Pitäjänmäki district. Emergency Services are investigating the incident in cooperation his Helsinki's Environment Centre.
The group director for paint manufacturer Teknos, Pekka Rantamäki, told Yle that solvent was accidentally pumped into a rain drainage sewer at one of its plants on Monday.
According to Rantamäki it was a case of human error. He was unable to estimate how much of the solvent had been discharged. He added that the problem was quickly noticed and the pump was shut down.
Years of efforts destroyed
Pekka Lindblad, a local resident, told Yle that the fumes from the spill were strong enough along the riverbank to have given him a headache. He was particularly distressed by the impact on the trout population.
Lindblad related that he has been involved for four years in efforts to clean up the river's environment to provide spawning grounds for highly endangered sea trout. This spring, trout spawn was introduced into the river in the hopes of reviving the population.
"This scene is depressing, the destruction is quite serious. It looks like most of the spawn introduced to the river have died. Luckily, some of them managed to make it to the sea. This came at such a bad time, since the trout hit breeding age after four years," Lindblad pointed out.
Helsinki police have begun a criminal investigation into the incident.