Canada's Goldstream River failed to live up to its name when its waters bizarrely started flowing a fluorescent Luminous green.
The river, which runs through the city of Langford in British Columbia, looked like the result of a radioactive disaster and an investigation was launched immediately.
What caused the river to change colour was a mystery at first, but investigators swiftly discovered an organic compound used as a dye to test water systems was to blame.
Colourful: The Goldstream River started flowing fluorescent green after hoaxers added an organic dye to the water
But as no tests were being conducted on the day the Goldstream River turned green, officials immediately pointed the finger at pranksters.
Tyson Elder was hiking along the river with friends photographing Bald Eagles when he saw the fluorescent green water on December 29.
Tyson, 24, from Victoria, British Columbia, said: 'In the distance all I could see was bright neon green - it looked like coolant.
'To see something so bright and unexpected was kind of unnerving, especially because it is a popular tourist destination.
'In the winter the Bald Eagles mate and nest there so we were worried about what it would do to the animals. Luckily tests showed it was not toxic.'
News of the neon-green waters spread fast after Tyson posted images on his Twitter site.
'Everyone was shocked by what they saw,' he said. 'It was big news. It was picked up by radio stations and people were flooding to the park.
'No-one seemed to know what was going on. It was quite an interesting day.'
Tyson, a photographer who also works in mediation, said the water ran green over a stretch of 400 metres for about three hours.
His friend had a camcorder and the video on YouTube has been viewed around 550,000 times.
Langford Fire Chief Bob Beckett blamed the greening of the river on unidentified pranksters.
'In all likelihood it's a hoax, but it's unfortunate we had to utilise all sorts of resources to investigate this,' he said.
Fluorescein, which is also used as a tracer in medical procedures, can cause allergic reactions, according to Vancouver Island Health Authority officials.
'It does not have a high toxicity, but it can cause allergic reactions,' said medical health officer Murray Fyfe.
Local resident Bruce Bradley, 27, said: 'It looked like the result of a radioactive disaster. I was half expecting to see two headed fish swimming about.
'It was quite incredible to see, it was really bright. A few guys were spooked by it all at first. It was bizarre.'
The substance is not believed to have affected fish populations, and according to the Montreal Gazette, the river turned back to its regular colour within an hour.