Authorities in Venice, Italy are investigating the source of a strange phosphorescent green liquid patch that appeared Sunday in the city’s famous Grand Canal. 

While no one has claimed responsibility for the water color change at the canal, there was an event in Rome last weekend staged by an environmentalist group that used a vegetable charcoal to turn the Trevi fountain's water black. The group claimed to act in response to the Italian government's climate policies.

Images and videos posted on social media show a bright patch of green in the canal along the populated areas of the city.

The city's fire department posted a video on Sunday as one of its boats journeyed on the waters and stated, "the Grand Canal colored in green is what the fire department found this morning as we intervened together with ARPAV to collect samples and analyze this abnormal color."

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Environmental authorities are working to determine what caused the water to turn bright green.

Venice's Interior Ministry's representative Michele di Bari and police are claiming that the bright green liquid does not pose a threat to the health of locals and tourists. 

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The governor of the Veneto region, Luca Zaia, posted a photo of the green liquid that spread through the water near the arched Rialto Bridge. The patch was reported by residents. Zaia said that officials had requested that the police investigate to determine who was behind the event.

The latest incident also sparked comparisons with an event in 1968 by Argentine artist García Uriburu who dyed the waters of the city's Grand Canal green in order to promote ecological awareness during the internationally recognized cultural festival, the Venice Biennale. 

The Associated Press contributed to his report.