It starts slowly, with sea water seeping up through drains in Piazza San Marco, covering the gray stone like rippled glass. An hour later, flooding has completely submerged the square.
Elevated wooden sidewalks are erected in a matter of minutes, and Venetians and tourists scurry along them in a frenzied rush that would give even New York subway riders pause.
Fed up with the traffic on the sidewalks, a few brave souls - mostly giddy tourists and a few rubber-boot-clad locals - hike up their pants and wade in.
So it goes each winter, during Venice's annual battle with the acqua alta, or high water.
For centuries, this city built on a shifting pile of mud has sunk as sea levels have risen. And for years, academics and environmentalists have wondered how to save it without destroying the surrounding lagoon.
Now, after extensive studies yielded a $2-billion project to keep the sea at bay, political wranglings and a new survey by researchers may scuttle it.
Called Project Moses, the plan was to use a series of submerged gates to seal off the Venetian lagoon from the Adriatic Sea when the sea rose more than three feet above the lagoon's normal level.
But a recently published report in the journal Antiquity says Venice is sinking at a rate of 10 inches per century - twice as fast as generally thought. That makes the gates useless, the researchers said.
Moreover, critics in Rome have called the plan too expensive and environmentally unsound.
Both here and elsewhere, few agree on the extent of the damage caused by the flooding, but all acknowledge that it is getting worse each year.
At the dawn of the 20th century, St. Mark's Square - the lowest point in Venice - flooded about seven times a year. Now, it floods as many as 100 times a year, and scientists say climate change will cause the Mediterranean to rise eight inches during the next half century, leaving Venice under water for half the year.
"At first I thought those walkways were to keep people from doing further damage to the crumbling buildings, but when we stepped out of the basilica and saw the water beginning to rise, I realized what they were for," says Jean Quine of Chevy Chase, Md., who vacationed with her family in Venice last October.
Her husband, Steve, recalls a Venetian traffic cop directing pedestrians on the wooden planks.
"He would allow so many people through on one side and then blow his whistle to stop them. Then he'd allow so many people through on the other side and blow his whistle again. It was the most chaotic thing," he says. "Finally I got fed up and jumped off."
Floating around the city in a gondola as women hang wash from windows and bright flowers drape cracked-plaster walls, it's easy to see why so much attention is being paid to the preservation of Venice.
Ten million tourists come each year to see the city's masterpieces. So far, none of the architectural or artistic wonders has been lost to the rising water. And while St. Mark's basilica leans a bit to the left because of the unstable earth and corrosive salt water, many visitors don't seem to mind.
The acqua alta simply adds more character.
"You can see how high the water has come when you take a gondola ride," says Mrs. Quine. "The water is slowly changing to the color of the stucco on the buildings. It adds to the charm."
(c) Copyright 2000. The Christian Science Publishing Society