The waters in Venice’s main canal turned fluorescent green on Sunday in the area near the Rialto bridge and authorities are seeking to trace the cause, Italy’s fire department said.

The regional environmental protection agency has received samples of the altered waters and is working to identify the substance that changed their color, the department said in a tweet, Reuters reported.

The Venice prefect has called an emergency meeting of police forces to understand what happened and study possible countermeasures, the Ansa news agency reported.

The incident echoes recent episodes in Italy where environmental groups have been coloring monuments, including using vegetable charcoal to turn the waters of Rome’s Trevi fountain black in a protest against fossil fuels.

However, unlike previous cases, no activist group has come forward to claim responsibility for what happened in Venice.

A British sailor’s boat was targeted on Thursday in the latest attack near Gibraltar, by Gladis, a killer whale and her gang of orcas.

Gladis, believed to be traumatized, is thought to be teaching other orcas to target boats.

So far this month there have been 20 attacks on small vessels sailing in the Strait of Gibraltar. However the Atlantic Orca Working Group (GTOA) have reported dozens of attacks on ships along the Spanish and Portuguese coasts this year.

Experts believe Gladis may have suffered a “critical moment of agony”, such as colliding with a boat or becoming entrapped during illegal fishing, which altered her behavior in a “defensive” fashion, the Independent reported.

“That traumatized orca is the one that started this behavior of physical contact with boats,” Dr Lopez Fernandez told Live Science.

“We do not interpret that the orcas are teaching the young, although the behavior has spread to the young vertically, simply by imitation, and later horizontally among them, because they consider it something important in their lives,” he said.

The behavior has baffled scientists, with some initially suggesting it could be related to the harmful scarcity of food facing the mammals, or the disruptive resumption of business-as-usual nautical activities in the wake of the pandemic, while others have suggested it could be playful behavior.

Although known as killer whales, endangered orcas are part of the dolphin family. They can measure up to eight meters and weigh up to six tonnes as adults.

Microsoft President Brad Smith said Thursday that his biggest concern around artificial intelligence was deep fakes, realistic looking but false content.

In a speech in Washington aimed at addressing the issue of how best to regulate AI, which went from wonky to widespread with the arrival of OpenAI’s ChatGPT, Smith called for steps to ensure that people know when a photo or video is real and when it is generated by AI, potentially for nefarious purposes, Reuters reported.

“We’re going have to address the issues around deep fakes. We’re going to have to address in particular what we worry about most foreign cyber influence operations, the kinds of activities that are already taking place by the Russian government, the Chinese, the Iranians,” he said.

“We need to take steps to protect against the alteration of legitimate content with an intent to deceive or defraud people through the use of AI.”

Smith also called for licensing for the most critical forms of AI with “obligations to protect security, physical security, cybersecurity, national security.”

“We will need a new generation of export controls, at least the evolution of the export controls we have, to ensure that these models are not stolen or not used in ways that would violate the country’s export control requirements,” he said.

For weeks, lawmakers in Washington have struggled with what laws to pass to control AI even as companies large and small have raced to bring increasingly versatile AI to market.