Venice -- city of canals, tourists, and priceless art -- is accustomed to the occasional high tide, but even by its own redoubtable standards, the flooding that began Monday is something out of the ordinary. According to the city's Tide Center, water levels climbed to 156 centimeters (61 inches), making it the worst case of flooding since 1986, when tides reached 159 centimeters.

"Acqua Alta!" was the warning emanating from loudspeakers beginning at 11 a.m. on Monday morning as Venetian officials struggled to convince the city's population to stay inside. In many of Venice's most popular spots, including St. Mark's Square, the tides reached up to people's thighs -- shallow enough for the most intrepid tourists to wade through, but deep enough for the city to worry about the risks of people going outdoors. Further complicating matters was an ill-timed strike among the Venice's famous vaporetto water buses.

The high water was caused by stormy weather and heavy rain over the weekend, But it was far from the city's worst flood on record. That honor goes to "The Great Flood" of 1966, when water levels reached as high as 194 cm, leaving about 5,000 people homeless and destroying countless works of art.

Although this time it looks like Venice will escape wide-scale damage, periodic floods are an increasing problem, and many researchers worry that global warming could make them more frequent still. Venice's complex island-structure lies just one meter above sea-level, and average water levels have risen 24 cm in the last 100 years. They're continuing to grow at an annual rate of 3 millimeters, though climate change could push that number upwards.