• The bright green patch was observed on the Grand Canal on Sunday morning
  • Water samples have already been taken to figure out what caused the change
  • Some speculate that a substance may have been poured into the canal

Venice's famous canals have long drawn the world's regard for its classic charms. Over the weekend, however, it captured people's attention for a different reason: It turned fluorescent green.

The bright green hue of the waters on the Grand Canal was reportedly sighted on Sunday morning. In a tweet, Veneto regional president Luca Zaia explained that residents close to the Rialto bridge spotted the fluorescent patch of water.

Authorities are already investigating the matter, Zaia further said as he shared a photo of the canal with the bright green patch of water clearly standing out.

What exactly caused the fluorescent hue is unclear. Some suggested that algae could be behind the discoloration, according to CNN. Such blooms have been known to alter the color of water, which can be seen even from space.

There were also those who began speculating that it might be due to a substance that had been poured into the canal, like when artist Nicolás García Uriburu dyed its waters in 1968 to raise awareness of the relationship between civilization and nature. The dye was "ecologically harmless," according to The Metropolitan Museum of Art. At the time, the waters remained fluorescent green until low tide, when it gradually turned back to normal.

So far, however, no one has claimed responsibility for the color change, even though there have been speculations that an environmental group may be behind it, CNN noted. Activist organization Ultima Generazione, for instance, which turned the Trevi fountain in Rome black last week in protest against fossil fuels, told the outlet that it was not behind the Canal's fluorescent coloration.

Why the Grand Canal turned fluorescent green remains unclear, but authorities have already collected samples to be tested, Italy's fire brigade, Vigili del Fuoco, said on Twitter. It also shared a photo of the brightly-colored waters.

Local authorities have also been looking at CCTV footage to see whether it may have been a part of a stunt, BBC News reported. Apparently, the sighting coincided with the Volgalonga regatta boat event — a peaceful protest for rowers against lagoon degradation and the damages from motor boats.

Indeed, the Grand Canal is no stranger to transformations. One can recall that in 2020, the waters in the canals became much clearer than usual amid the drop in traffic and tourists because of the COVID-19 pandemic.

Tourists look across the Grand Canal while on the Rialto Bridge in Venice in 2011. Residents of the famed city say the rising number of ill-behaved visitors is turning their home into Disneyland. Getty Images