Officials said the mystery behind the bright green waters of the Venice Canal has been resolved

Environmental officials in Italy say they have solved a mystery that turned the waterways of Venice’s historic canal a bright shade of green.

On Sunday, Venetians reported that the water in the canal up to the Rialto Bridge had turned fluorescent green, prompting a police investigation.

Environmental authorities conducted chemical and biological tests on the water and discovered that the bright green color was caused by the presence of fluorescein, a non-toxic substance used to test sewage networks, according to a press release issued by the Veneto Regional Agency for Prevention and Environmental Protection.

Pictures circulating on social media showed the famous canal lined with restaurants and tourists in shades of emerald. It appears that water taxis, gondolas and water buses continued to operate as usual, despite the unusual tint of the canal.

The water was so green that it appeared to be a similar color to the Chicago River during the annual tradition of dyeing the waterway green to celebrate St. Patrick’s Day.

The origin of the material was not disclosed. Officials said more tests are expected this week.

Investigators initially thought the green channel could be another ploy by environmentalists.

Activists from the Italian environmental group Ultima Generazione, which translates to “last generation,” Black liquid poured out At the Trevi Fountain in Rome on May 21 to protest the use of fossil fuels. Two days later, two last-generation protesters smeared themselves with mud outside the Senate building in Rome to remind the public of the country’s flood risks linked to climate change.

The demonstration is one of the latest acts of environmental vandalism activists have engaged in to draw attention to the causes they support by targeting priceless landmarks and artworks around the world.

Van Gogh’s “Sunflowers” at the National Gallery in London, Monet’s at the Barberini Museum in Potsdam, Germany, and the famous painting “Girl with a Pearl Earring” at the Mauritius Museum in the Netherlands have all been targets of environmental vandalism in the past year. The display methods included throwing foods such as tomato soup and mashed potatoes and sticking hands to the frames of paintings.

The trend is out of desperation for what the planet will look like in the future, experts in climate and environmental psychology told ABC News.

ABC News’ Will Gretsky contributed to this report.