The toxic red sludge that spilled from an alumina plant on Monday has reached the Danube River threatening the water supplies for millions of people across Europe.
The by-product from the early stage of aluminium production the sludge has caused pH levels in the river to soar to at least 8.4 in the Danube and peaking at 9.65 in the Mosoni-Danube area.
Authorities have been dumping clay and acid into the river to bring pH levels down towards water's natural pH level of 7.0 to save the eco-system.
However experts worry the sludge will contaminate groundwater and underground reservoirs.
Contact with the substance can burn skin while ingesting it can result in death or cause lung and intestinal damage.
The Danube River is Europe's second-longest river.