VENICE, ITALY - AUGUST 11: A Gondola sails the Grand Canal in front of a busy Rialto bridge on August 11, 2011 in Venice, Italy. Italian heritage group Italia Nostra warned that Venice is facing an irreversible environmental catastrophe unless visitor numbers are capped. The acceptable maximum number of tourists for Venice is 33,000. In 2011 the average number of visitors to the city daily is 60,000 that is too high for such a fragile city and is causing the gradual destruction of the lagoon ecosystem.