BUCHAREST, Oct 7 The toxic red sludge that burst out of a Hungarian factory's reservoir reached the mighty Danube on Thursday after wreaking havoc on smaller rivers and creeks, and downstream nations rushed to test their water for contamination.

The European Union and environmental officials fear an environmental catastrophe affecting half a dozen nations if the red sludge, a waste product of making aluminium, contaminates the Danube, Europe's second-longest river.

Officials from Croatia, Serbia and Romania were taking river samples every few hours on Thursday but hoping that the Danube's huge volume would blunt the impact of the spill.

The Hungarian reservoir break on Monday disgorged a toxic torrent through three villages and creeks that flow into waterways connected to the Danube. Creeks in Kolontar, the western village closest to the spill site, were still swollen and ochre red days later and villagers said they were devoid of fish.

The red sludge reached the western branch of the Danube on Thursday morning and its broad, main stretch by noon, Hungarian rescue agency spokesman Tibor Dobson told the state MTI news agency.

Dobson said the pH content of the red sludge entering the Danube had dropped and was unlikely to cause further environmental damage. It had been tested earlier at a pH level of 13 and now was down under 10, and no dead fish had been spotted in the Danube, he said.

A neutral pH level for water is 7, with normal readings ranging from 6.5 to 8.5. Each pH number is 10 times the previous level, so a pH of 13 is 1,000 times more alkaline than a pH of 10.

The sludge has devastated local waterways.

“Life in the Marcal River has been extinguished,” Dobson said, referring to the river's 40km stretch that carried the red waste from Kolontar into the Raba River and onto the Danube.

He said emergency crews were pouring plaster and acetic acid (vinegar) into the Raba-Danube meeting point to lower the slurry's pH value. “The main effort is now being concentrated on the Raba and the Danube,” he said.—AP