VENICE -- Four months ago Mirella Dalla Pasqua, born and raised in this venerable city improbably built on water, did something she thought she would never do: She bought a house on the mainland.
``I had no choice," said Dalla Pasqua, 31, who described leaving for the ``terra firma" side of the lagoon as a trauma. ``I'm proud to be a Venetian," she said, but ``house prices are impossibly high in Venice, and then you have to fix them up. Young people just can't afford that."
Over the past 50 years, thousands have taken part in a collective disappearing act. From a peak of 171,000 residents in 1951, the population of the historic center of Venice has fallen to 62,000.
``We've reached the point of collapse, the point where things could fall apart," said Ezio Micelli, an urban planner.
Should the trend continue, newspapers fretted recently, by 2030 authentic Venetians could become extinct and the historic center reduced to a shell subsisting only on tourism.
According to recent estimates, 15 million to 18 million tourists have visited Venice over the last year. On some days they easily outnumber residents.
When the ratio of tourists to residents tips in favor of the former, ``it's not meaningful to talk about Venice as a city anymore," said Robert Davis, a professor of Italian history at Ohio State University. ``The city is basically already lost. The speculation is what will happen to it next."
Venice is now largely dependent on tourism for its economic survival, even as tourists complicate daily life for most Venetians
``You can't get onto a vaporetto" -- the public transport boat that ferries people around the canals -- ``without finding it packed with tourists and their suitcases," said Gianpietro Meneghetti, a retired bank manager.
The price of property is exceptionally high in Venice, with a 328-square-foot apartment going for up to $1.23 million.
Something must be done to ``stop the exodus and protect the resident population," said Mayor Massimo Cacciari .
Through a municipal real estate development agency, the city is building 500 to 600 apartments that it will rent to middle-class families, the social group at greatest risk of ``extinction."
``If you lose the middle class, you end up with polarization between the very rich and the very poor, and the city becomes unglued and falls apart," said Micelli, the urban planner.
Similar projects in other areas of Venice have been successful, he said, slowing the exodus to the mainland.
The Venetian authorities also want to lure new residents to the historic center and are looking to develop job opportunities beyond the tourist industry.
The city is pressing its cultural advantages, boosting research facilities and university programs as well as promoting cultural events like the Biennale art exhibition and film festival.
Cacciari is also seeking to make tourism help pay for the city. He is trying to impose a tourist tax and to get locals who make money from tourism to compensate the city for the burden they place on local services. Such taxes are not likely to keep tourists away.
``The demand for Venice is inflexible -- rising prices won't stop it," Davis said. ``People will come anyway."