The river, which runs through the city of Langford, British Columbia, turned a fluorescent green on Dec. 30, when a passer-by captured stunning video of the verdant waterway.
At first it wasn't clear what caused the river -- and the water in a nearby fountain -- to change color. But investigators now believe that the green hue was caused by the addition of fluorescein, a synthetic organic compound that is often used as a dye, or a "fluorescent tracer," in the testing of water systems.
On the day that the Goldstream River turned green, officials were not conducting any tests of the waterway that involved fluorescein.
Langford Fire Chief Bob Beckett blames the temporary greening of the river on unidentified pranksters.
"In all likelihood it's a hoax. It may be a nontoxic substance, but it's unfortunate that we had to utilize all sorts of resources to investigate this," Beckett told CTVBC.ca.
Fluorescein, which is also used as a tracer in medical procedures, can cause some people to suffer allergic reactions, Vancouver Island Health Authority officials told the Times Colonist.
"It does not have a high toxicity, but it can, rarely, cause allergic reactions," said medical health officer Murray Fyfe. "People who do have a sensitivity should take precautions and avoid contact."
The substance is not believed to have negatively affected fish populations, and according to the Montreal Gazette, the river turned back to its regular color within an hour.
Read more at CTVBC.ca, the Times Colonist and the Montreal Gazette.