- A patch of water turned bright green in Venice's canal on Sunday.
- Police have launched an investigation to find out why the water changed color.
A patch of Venice's famed Grand Canal turned fluorescent green Sunday, and no one is sure why.
The strange sighting was first spotted by locals in the Italian city, according to Veneto region's president, Luca Zaia.
"The prefect has called an urgent meeting with the police to investigate the origin of the liquid," he tweeted.
Local councils took water samples, examined CCTV footage, and questioned gondola drivers to find out if they had seen anything suspicious, CNN reported.
The Italian fire service has also been working with the Regional Agency for Environmental Protection to test water samples, according to the Guardian.
So far, online speculation has ranged from climate activists causing the change to algae creating a color shift.
Maurizio Vesco, from the Regional Agency, told Italian newspaper La Repubblica that the growing streak of green was likely caused by fluorescein, which is a safe test dye. He suspected that up to a kilogram of the dye could have been poured into the canal.
City councilman Andrea Pegoraro pointed to environmental activists as the potential culprits in the wake of recent protests on Italian cultural sites.
Environmental activist group Ultima Generazione covered Rome's Trevi fountain with black liquid last week, while in March, activists spray painted the walls of Florence's town hall orange to bring attention to climate change.
No environmental group has so far claimed responsibility for the incident.
If eco-warriors are responsible for the change in color, it wouldn't be the first time.In 1968, Argentine artist Nicolás García Uriburu dyed the waters of the canal a fluorescent green to make a statement about ecological issues in the region.