Last Sunday, Venetians and visitors alike woke up to a strange scene, something that appeared to belong more in the Emerald City of Oz than the Italian metropolis: Venice’s Grand Canal was green. While the cause of the verdant channel was not originally known, city officials have now identified fluorescein, a chemical most often used in underwater construction, as the reasoning, reports CNN. However, it’s still unclear why or how the substance made its way into the water.
Residents first noticed a fluorescent green patch near the Rialto Bridge on Sunday, which appeared to spread as the day went on. Luca Zaia, the governor of the Veneto region, tweeted at the time that the government had called an urgent meeting to identify the source and that police were investigating the matter. Before determining that it was fluorescein in the water, multiple theories had circulated online, including some blaming algae growth as the cause.
Fluorescein is not toxic, but its appearance raises questions. “No danger of pollution from the fluorescent green patch that appeared yesterday morning in the waters of Venice, but the risk of emulation is worrying,” Zaia later tweeted on Monday morning. “Unfortunately Venice has become the stage for actions far beyond the lines: adequate and strong responses are needed.”
Though no group has claimed responsibility, some have speculated that climate activists were involved in the incident. According to CNN, police are investigating a series of leads, and further test results from the water are expected later this week. Many have drawn parallels between last week’s event with an occurrence that took place 55 years prior. In 1968, Nicolás García Uriburu, an artist from Argentina, dyed the Grand Canal green during the Venice Biennale to promote ecological consciousness. Uriburu had also used fluorescein to carry out his work, which was not officially part of the cultural festival’s programming.
This article was originally published on Architectural Digest.