Pigeons and uncouth tourists are just the start of the Lagoon City's problems, writes Nick Squires.
They are to St Mark's Square what ravens are to the Tower of London. And now, Venice's pigeons, which have delighted generations of tourists, are all but gone. Europe's most beautiful city has decreed that they pose a health hazard to visitors and damage centuries-old palaces and statues with their highly acidic droppings. After deciding in May to ban the vendors who sold grain to tourists wanting to feed the birds, Venice's guardians have declared the move a success.
The pigeon population of St Mark's Square has been reduced from an estimated high of 20,000 to barely a thousand, they claim, after introducing a fine of EUR50 ($99) for anyone ignoring the ban.
"Just a few months after the feed ban most of the square is free of the animals, which have moved off to find food on surrounding islands," said Renata Codello, Venice's superintendent of architectural and cultural heritage.
The pigeons had "almost completely disappeared" from the Doge's Palace, once their favourite place to gather. The battle against the birds is just one front in a two-year crusade to spruce up the Lagoon City by cracking down on dirt, litter and poorly behaved tourists.
Budget airlines have put Venice within reach of millions of tourists but all too often Venetians are appalled at the way visitors conduct themselves.
As Henry James observed more than 100 years ago: "Though there are some disagreeable things in Venice, there is nothing so disagreeable as the visitors."
Each year, Venice's embattled 60,000 inhabitants are swamped by a staggering 20 million tourists.
In an attempt to reduce friction between locals and the flood of visitors, Venice formed a band of young women called City Angels to crack down on the sometimes uncouth behaviour of tourists.
They politely ask daytrippers not to expose too much flesh by wandering around shirtless, not to dangle their feet in fountains and not to hold picnics beside centuries-old monuments.
This month the campaign stepped up a notch, with a fresh range of initiatives announced by Venice's comune, or city council, to try to keep the ravages of mass tourism at bay.
As the winter tourism season starts, large posters asking visitors to "Keep the City Clean" ("Tenere La Citta Pulita" in Italian) are to be placed in prominent spots.
Visitors using "vaporetti" (water buses) will be reminded to give up their seats for elderly people and pregnant women, while backpackers will be urged to remove their unwieldy bags before boarding.
Fare dodgers will also be targeted, promises the city's "clean-up czar", Augusto Salvadori, who as councillor for tourism has been charged with improving "public decorum" in "La Serenissima", as Venice is known.
"The fight against fare dodgers will be unrelenting," Salvadori says. "In the future, you won't be able to board without showing your ticket to the inspector and we're studying the possibility of installing turnstiles."
While Venice has succeeded in smartening up its image, it still faces a range of threats to its long-term survival.
The Unesco World Heritage Site is in danger of having any semblance of "normal" life squeezed out of it.
Soaring rents and property prices - it is the most expensive city in Italy after Rome - mean Venetians can no longer afford to live in the city.
In the past 40 years the population has halved, from 120,000 in 1966 to 60,000. A quarter of those residents are older than 64 and the city's registry office has warned that Venice could be devoid of inhabitants by 2030.
"The demographic trend is negative because more people are dying than are being born," says Mara Rumiz, a city councillor who is in charge of housing.
The demand for tourist accommodation is so insatiable that property owners are turning their homes into bed and breakfasts, further squeezing out locals.
In the past six years, the number of properties turned into hotels and B&Bs has increased more than fourfold. The city runs the risk of becoming a kind of historical and architectural Disneyland, admired by hordes of slack-jawed tourists by day but abandoned as a virtual ghost town by night.
One of Italy's biggest newspapers, La Repubblica, speculated: "They'll open the gates in the morning and close them in the evening."
Councillor Rumiz says Venice is staunching the exodus of locals by promoting businesses other than tourism, such as education (the city already accommodates 20,000 students), information technology and boatbuilding.
"Venice will never be Disneyland," she says. "It's a normal city, which just happens to have an extraordinary cultural heritage.
"Only the stupidest tourist could love a city in which there is no normal life. Tourism must not be the only economic activity."
As a city surrounded by water and criss-crossed by canals, Venice is also uniquely vulnerable to climate change and rising sea levels. A century ago, St Mark's Square flooded about 10 times a year; that figure has risen to about 60.
After years of indecision, a system of moveable flood barriers known as MOSE (Modulo Sperimentale Elettromeccanico) is being installed to protect the city. The Intergovernmental Panel on Climate Change has put forward a worst-case scenario in which global sea levels could rise up to 88 centimetres before the end of the century. If that happens, the Adriatic Sea would consume Venice.