Local officials say that there is nothing to fear, as the color was caused by a harmless dye added to the river to aid in investigating a Catalonia water bottling plant. The plant has been linked to an outbreak of gastroenteritis last year that left thousands sick after they drank from contaminated office water coolers.

Albert Batalla, the mayor of Seu d'Urgell, a city near where the Gran Valira River empties into the Segre River, has assured residents that the dye is "entirely harmless, non-toxic and biodegradable."

Similarly, the Andorran Ministry of Health released a statement saying that "it is an action that has no impact beyond the visual," and "was safe for both people and the environment."