Giancarlo Galan, the centre-right governor of the northeastern Veneto region, which includes Venice, has complained of 'a frightful increase' in the number of seagulls, and of 'thousands' of plastic bottles floating in the canals.

'With the sea-gulls what can I do? Should I use a machine gun? All seafront cities have this problem,' Cacciari said.

The mayor admitted plastic bottles are a problem, but said the Venice town hall is still awaiting from the central government some 50 million euros in promised funds for the city's upkeep.

In 2007 an estimated 21 million tourists visited Venice.