Hungary has officially asked the European Union for help as it takles what its president has described as an “ecological tragedy”.
All life in the one river has been “extinguished” according to a disaster official.
The most immediate danger is the high alkalinity caused by Monday’s toxic red sludge spill.
Crews have been pouring plaster and acetic acid into waterways to try to bring pH levels down.
The sludge has now reached the River Danube – a water mass large enough to dilute the toxicity a little – but countries downstream like Croatia and Serbia are drawing up emergency plans nevertheless.
In Kolontar, where four people died and dozens were injured as the caustic waste passed through, the situation is still dangerous.
It is feared that as the sludge dries the silicon oxide in it could turn into a dust that can cause lung disease and cancer.
The clean-up operation is almost unimaginably huge – virtually everyone and everything has been affected.