A patch of bright green water that materialized in Venice’s Grand Canal on Sunday was caused by a non-toxic chemical used for testing wastewater networks, regional environmental officials said. It was not immediately clear how the chemical, fluorescein, wound up in the water under the Rialto Bridge. A press release from the Regional Agency for the Environment in Venice noted that it seemed to be a deliberate act, given the volume of chemical released. The Venice Police’s investigation into the bizarre matter remains ongoing, with speculation that it may have been a stunt by environmental activists. No organization had claimed responsibility for the act as of Tuesday. Earlier this month, Italian environmental group Ultima Generazione poured black liquid into Rome’s famed Trevi Fountain to protest the use of fossil fuels. When asked about the green blob in Venice by CNN on Monday, the group said, “It wasn’t us.” Further tests to determine “the nature of the substance in the water” are expected later this week.