Talvivaara staff halted the latest runoff of waste water from the nickel mine in north-eastern Finland on Tuesday after the River Lumijoki near the mine turned red and orange.
The discoloration extended several kilometres south of the mine.
The company blames a problem with sedimentation of iron at the Kortelampi neutralisation pond.
“The colour in the water is basically an aesthetic problem,” says the company’s communications director, Olli-Pekka Nissinen. “Iron and manganese are very effective at colouring water.”
The release of waste water has been suspended until the reason for the discolouration is ascertained. Nissinen says that the heavy metal content of the water has not rise and that its pH levels are normal.
The problem began on Tuesday. Nissinen says that there was no sign of discoloration in water samples taken in the morning.
Conservation group: "Outrageous"
The Kainuu chapter of the Finnish Association for Nature Conservation (FANC) is highly sceptical about the firm’s explanations. It has already submitted water samples for analysis.
“According to reports from the field, the colour of the water corresponds to that during the gypsum pond leak last November,” says Janne Kumpulainen, head of the local FANC branch.
“I think the company’s downplaying of this is outrageous and follows its usual procedures when it thinks that there is no evidence to contradict its word. Our own samples have already been sent to a laboratory,” adds Kumpulainen.