Why has Venice’s Grand Canal turned bright green?

An area of Venice’s famous Grand Canal has turned fluorescent green due to the presence of fluorescein – a chemical commonly used in underwater construction to help identify leaks, Italian authorities say.

Last weekend (28 May 2023), residents of Venice took to Twitter after an area of phosphorescent green water was spotted near the Rialto Bridge in Venice. Authorities were called, and environmental agencies began investigating the source of the bright green water.

Italy’s national fire department confirmed the authorities were working over the weekend to discover why the patch of water was discoloured.

Following samples of the water being taken, the Regional Agency for Environmental Prevention and Protection of Veneto (Arpav) confirmed on Monday (29 May) that the fluorescent green patch of water on Venice’s Grand Canal was due to fluorescein, a non-toxic substance used for testing water networks. 

CNN reported on Monday (29 May 2023), that it remains unclear how the substance ended up in the canal, but Arpav said that given the volume released, the colouring was likely to be intentional.

Several leads are currently being pursued, including the possibility of environmental activism.

Further tests are expected to be carried out later this week.

The investigation has involved police, the regional environmental agency and other local bodies.

Northern Italy is currently experiencing an extended period of drought, with water storage levels in parts of Italy currently less than half their normal levels. In February, MIN reported that the historic canal network in Venice had been hit by unusually low tides — reducing some canals to little more than a muddy ditch and leaving gondolas stranded.