But there is nothing to worry about as officials confirmed that the colour was due to a dye added to the water by the local administration. "The dye was entirely harmless, non-toxic and biodegradable and had been used as part of an investigation at a nearby water bottling plant", said the mayor in a statement.
Last year, thousands of people in Catalonia region of Spain fell sick after drinking contaminated water from the water plant. The dye was being used to identify the source of contamination, said the health ministry.
Panic-stricken residents shared photos of the slimy green river on social media
To everyone's relief, the river was back to its natural colour within a few days.