The Valira River in Spain turns green and scares residents.
Frozen trees are seen on the banks of the Pisuerga river in Santovenia de Pisuerga, Spain on Dec. 31, 2016. REUTERS

The Valira River in Spain turned bright emerald green Thursday, according to reports, causing concern amongst residents in the small town of Seu d’Urgell. Despite the shocking green color of the water, the town’s Mayor Albert Batalla assured citizens that the water was not toxic.

In a statement, the mayor explained environmentalists were testing the water during an investigation on a nearby water bottling plant, The Local, a Spanish news site, reported. During the test, which was issued to determine whether or not the water was “safe for both people and the environment,” green dye was added to the water, resulting in the fluorescent color.

The investigation followed an outbreak of a gastroenteritis bug that left thousands of people in Catalonia and northeastern Spain sick in 2016. The bug was traced back to a water bottling plant at the time, which is located near Seu d’Urgell, resulting in officials' decision to administer regular investigations of the plant and its effects on water in the environment.

Batalla said that the dye was “entirely harmless, non-toxic and biodegradable” and that residents had nothing to be scared of.

Along with the Seu d’Urgell mayor, Andorra’s Ministry of Health also confirmed that the dye was used to test the water for contamination.

The Valira River flows down from the Pyrennes Mountains into Andorra and then veers off into Spain where it empties into the Segre River in Seu d’Urgell.

This isn’t the first time a river has turned green and scared people. In 2010, Canadian residents were alarmed after the Goldstream River in Victoria mysteriously turned bright green. Following testing, officials determined that the water had not been contaminated and no wildlife had been affected by the neon green color. The coloring only lasted for about an hour, causing officials to believe the coloring was just an “act of vandalism” done by pranksters.