River turns bright green to the horror of residents Chicagoans might be green with envy, but this region is still aghast.

LONDON -- St. Patrick’s Day may be right around the corner but residents living along a river in the Pyrenees mountains were hardly feeling festive after discovering that the Gran Valira River, which runs through Andorra and northeastern Spain, had turned emerald green this week.

Officials in both countries attempted to reassure residents alarmed by the fluorescent color of the river, which had turned green Thursday at its source in Andorra and further downstream into the Catalonia region of Spain.

A harmless dye had intentionally been added to the river, the Andorran Ministry of Health said a statement. "It is an action that has no impact beyond the visual," the ministry said, adding that the substance was harmless to both people and the natural environment and would dissolve in a few hours.

Albert Batalla, the mayor of Seu d’Urgell, one of the Spanish towns on the river’s banks, confirmed the information in a statement, explaining that the dye was being used to investigate a water bottling plant. "It is a harmless, non-toxic and bio-degradable dye that has been used for a water research,’’ he wrote.

The plant was reportedly linked to a gastroenteritis outbreak in Catalonia last year that left thousands of people sick after they drank from contaminated office water coolers.

Images of the river have caused consternation on social media, where photos of the vivid green water have been posted by residents.

Indeed, Chicago might be the only place where a river’s suddenly turning bright green might not greeted with alarm by residents; the city has an annual tradition of dying the Chicago River green the Saturday before St. Patrick’s Day, which is in two weeks.