A toxic red sludge spill from a metals plant that has wiped out all life from one Hungarian river has entered the Danube, one of Europe's largest waterways.
Dead fish were sighted in the Mosoni-Danube, a southern branch of the river, on Thursday and officials said that the Marcal, a tributary to the waterway, had been devastated by the sludge.
"The entire ecosystem of the Marcal river has been destroyed, because the very high alkaline levels have killed everything," Tibor Dobson, a spokesman for Hungary's disaster agency, told the Hungarian news agency MTI.
"All the fish are dead and we haven't been able to save the vegetation either," he said.
Residents have also reported local streams to be empty of wildlife.
The corrosive waste, which has high alkaline levels and could contain heavy metals, entered the Danube at around midday local time (10:00 GMT) on Thursday, disaster relief services said.
However, Emil Janak, the director of the regional water authority, sought to allay fears about the impact the toxic spill would have on the Danube.
"Alkaline levels show that the pollution will probably not have an effect on the Danube's ecosystem below Komarom," he was quoted as saying by MTI news agency.
The city of Komarom is 20km downstream of the area where the red sludge is entering the Danube.
"The fish are edible and the waters are quite drinkable," Janak said.
Countries downstream, including Croatia, Serbia and Romania, are ramping up water quality controls in towns along the river over fears of contaminated supplies.
"If we have the slightest indication that the Danube's waters are polluted on entering Romanian territory we will immediately impose a full restriction on drinking water supplies from the river," Adrian Draghici, the head of a regional water management authority in Romania said.
Emergency crews in Hungary were pouring hundreds of tonnes of plaster and acetic acid into the rivers to neutralise the alkalinity on Thursday.
Timea Petroczi, a spokeswoman for the disaster relief services, said that efforts to neutralise the pollution were "already getting good results showing that alkaline levels in the water are falling".
"We've got 500 people involved in the clean-up today. We're using high-pressure water jets to clean roads and houses."
Gabor Figeczky, Hungarian branch director of the WWF environmental group, said that it seemed that the efforts would be enough to stop the pollution spreading beyond Hungary's borders.
"Based on our current estimates, it [pollution] will remain contained in Hungary, and we also trust that it will reach Budapest with acceptable pH values," he said.
But fears remain that the sludge could have long-term implications for the 1,775-mile Danube, which flows through Croatia, Serbia, Romania, Bulgaria, Ukraine and Moldova before emptying into the Black Sea.
"It is important that we do ... everything possible that it would not endanger the Danube," Janez Potocnik, the EU environment commissioner, told The Associated Press news agency in Brussels, Belgium.
|Local residents have been collecting dead fish in the Marcal river, killed by the red sludge [AFP]
Viktor Orban, Hungary's prime minister, has described the spill as a natural disaster unprecedented in Hungary.
"If this had happened at night then everyone here would have died," he said as he visited on of the three villages devastated as a torrent of toxic mud swept them after a reservoir at the Ajkai Timfoldgyar Zrt metals plant in Ajka burst open on Monday.
"This is so irresponsible that it is impossible to find words!"
At least four people were killed and another 120 injured. Three people are still missing.
Many have suffered from burns and eye irritations caused by corrosive elements in the mud, and hundreds have been evacuated from their homes.
MAL Zrt, the company that owns the metals plant, said the waste was not considered hazardous under EU standards and recommended people clean off the sludge with water.
But Anita McNaught, Al Jazeera's correspondent in Kolontar, one of the villages affected by the spill, said the claim was a bit of a "semantics game".
"The red sludge is not classified as hazardous waste per se, but the EU said today, that does not mean it is not toxic and does not mean it is not dangerous, because very clearly, it is both," she said.
The European Union said on Wednesday that it feared the disaster could spread to half a dozen European nations and was ready to offer help.
Hungary's national disasters unit defined the red mud on its website as: "A by-product of alumina production".
"The thick, highly alkaline substance has a caustic effect on the skin. The sludge contains heavy metals, such as lead, and is slightly radioactive. Inhaling its dust can cause lung cancer."
Greenpeace was warned that the sludge spill is "one of the top three environmental disasters in Europe in the last 20 or 30 years", Herwit Schuster, a spokesman for the group, said.
Authorities have ordered a criminal inquiry into the accident.
Jozsef Deak, the company's operations manager, said it would not shy away from taking responsibility if found guilty.