Tourists and residents were shocked when the water near the iconic Rialto Bridge in Venice, Italy, turned bright green over the weekend. Authorities tested the water and found it was contaminated with fluorescein, a non-toxic organic dye used to identify leaks in underwater construction.
The local police said they are awaiting the results of additional tests and are conducting an investigation to determine who is responsible for turning the water green.
Investigators have not said how the chemical ended up in the water. While officials believe it could be the work of an environmental activist group, no organization has claimed responsibility.
A spokesperson for the group Ultima Generazione told CNN they were not responsible. Last weekend, the group claimed responsibility after members poured charcoal into the Trevi Fountain in Rome.
This was not the first time the Venice canals had turned green. In 1968, artist Nicolás García Uriburu used fluorescein to dye the water green to bring awareness to ecological issues facing the planet.