Russian authorities have collected nearly 30 tonnes of oil that spilled into the Yenisei river following the deadly power plant accident in Siberia, an emergency ministry spokeswoman said Thursday.

"From the start of an operation to eliminate the consequences of the catastrophe, a total of 29 tonnes of oil have been collected," said Irina Butenko, a spokeswoman for the emergency situations ministry in the Khakassia region, scene of the August 17 tragedy.

She said it was hard to predict how much more oil would have to be collected. "No one knows how much has leaked," she said.

An oil slick of 130 kilometers (80 miles) had spread along the Yenisei River after the disaster that killed 17 people and left 58 missing, the Ria-Novosti news agency reported Thursday.

The slick has been blamed on transformer fluid which is believed to have leaked from one of the hydroelectric station's units damaged during the accident.

The plant contained a total of 500 tonnes of oil, Ria-Novosti said.

Natural Reesources Minister Yury Trutnev however sought to dismiss doom-and-gloom reports, saying in televised comments, "I believe there are no grounds to speak of an environmental disaster."

Alexei Knizhnikov, head of the WWF Russian programme for the oil and gas sector, said trout farms located downstream from the dam were endangered and up to 400 tonnes of the fish might be dead.

Monday's catastrophe is believed to have been triggered when a technical problem caused a massive surge of water to erupt into the turbine hall, engulfing around 100 workers.