According to the head of Hungary's local disaster relief service, a toxic sludge spill has reached the Danube River, the second longest in Europe, and killed all life in a smaller river called the Marcal.

"I can confirm that we have seen sporadic losses of fish in the main branch of the Danube," regional chief for the disaster relief services Tibor Dobson told news agency Agence France-Presse.

"The fish have been sighted at the confluence of the Raba with the Danube," where water samples had shown a pH value of 9.1, he said. "Fish cannot survive at pH 9.1," the official added.

Dobson added that "the entire ecosystem of the Marcal River has been destroyed ... the very high alkaline levels have killed everything. All the fish are dead and we haven't been able to save the vegetation either."

He added that water alkalinity, a measure of river contamination, was already above normal in the major waterway.

"[Thursday] morning, the pH level stood at 9.3. The experts are still measuring the pollution levels..." Dobson said, adding that pH levels of around 8.0 are considered normal at the Gyor section of the river.

Officials say it will take years to clean up the mess

The spill resulted in the deaths of four people, as well as over 100 injuries.

Gabor Figeczky, acting head of environmental group WWF in Hungary, told Deutsche Welle the spill threatens to kill off still more of the Danube's ecosystem.

"Now the spill has gotten through to the Raba River and then to the Danube, and it still has a much higher alkaline concentration that we saw before. So it's much worse than we expected [Wednesday]," he said.

'Man-made catastrophe'

The area around Ajka, in western Hungary, was inundated with the sludge after the walls of the Ajkai aluminia refinery's residue reservoir, about 160 kilometers southwest of Budapest, broke on Monday. The plant produces alumina, which is used in the smelting of aluminum.

The red mud is a toxic residue left over from the plant's aluminum production. It is slightly radioactive, highly corrosive and contains toxic heavy metals such as lead, cadmium, arsenic and chromium. It destroyed all vegetation other than trees and seeped into hundreds of houses in seven villages, leaving residents unsure of when they would be able to return to their homes.

Environment State Secretary Zoltan Illes said there was suspicion that the Hungarian Aluminum Production and Trade Company (MAL), which owns the Ajka reservoir, had stored more red sludge in the reservoir than was allowed, and that its walls had displayed stress fractures prior to the spill.

The spill occured near the town of Ajka

Figeczky from WWF, meanwhile, said the spill can likely be put down to human error.

"What we know is that there was no natural disaster, so there must have been some kind of human mistake made," he said. "These dams are built in such a poor manner because there are no real strict criteria for these kinds of dams, and this led to the sliding of one of the walls.

"The other thing is that I'm not sure the regular checks made by the authorities were strict enough," he added.

MAL chief Zoltan Bakonyi insisted, however, that the company had done nothing wrong, adding that it would suspend all production for the time being.

Prime Minister Viktor Orban, who has visited the affected region, expressed condolences to the victims' families and promised a thorough investigation to determine "who is responsible for this man-made catastrophe."

Author: Darren Mara, Gabriel Borrud (Reuters/AFP/dpa)

Editor: Nancy Isenson