But the culprit behind the dye remains a mystery. The Regional Agency for the Environment in Venice said the coloring was likely intentional because the amount was too large to be an accidental spill, according to the news network.
Officials are pursuing several leads, including the possibility of environmental activism, Venice police told CNN.
The phosphorescent green was noticed spreading Sunday near the arched Rialto Bridge, according to The Associated Press. Luca Zaia, the governor of the Veneto region, inspired curiosity by posting a photo of the water after it was reported by residents, the wire service wrote.
NPR noted that the contamination coincided suspiciously with an annual rowing race that “aims to celebrate the Venetian lagoon environment as well as to protest wave motion from excessive motorboat traffic that riles the city.”
The canal has been tinted in the past to make a statement.
In 1968, eco-artist Nicolas Garcia Uriburu used fluorescein to turn the Grand Canal green to “promote environmental awareness,” NPR wrote.