<p><strong>Floods in <a href="http://travel.nationalgeographic.com/travel/city-guides/venice-italy/">Venice</a> usually mean breaking out the waders, but a few adventurous souls in St. Mark's Square threw in the towel Sunday and stripped down to swimsuits. </strong></p><p>It's normal for <a href="http://travel.nationalgeographic.com/travel/countries/italy-guide/">Italy</a>'s "eternal city" to flood in winter, but Sunday's 5-foot (1.5-meter) inundation is the sixth highest since record-keeping began in 1872, according to the Reuters news service. (Interactive map: See how much of <a href="http://ngm.nationalgeographic.com/2009/08/venice/venice-animation">Venice floods at different water heights</a>.)</p><p>"Usually flooding occurs when there is high tides and rain." Recently "strong winds from the south further enhanced the high-tide conditions," explained <a href="http://www.rsmas.miami.edu/users/swdowinski/bio.html">Shimon Wdowinski</a>, a geophysicist at the University of Miami.</p><p>Most parts of Venice don't flood during the <em>acqua alta </em>("high water"), but on Monday three-quarters of the city was underwater. As of Tuesday, the water level has begun to recede, but it may take a while, Wdowinski said. "Venice sits in a lagoon that has three outlets to the Adriatic Sea. In cases of heavy rain, like now, it takes time for the water to flow out."</p><p>A barrier to protect the city from repeated winter flooding—known as the <a href="http://www.salve.it/uk/soluzioni/acque/f_mose.htm">MOSE project</a> —is due to be finished by 2014. Until then, "there's not much that can be done," Wdowinski said. (See <a href="http://news.nationalgeographic.com/news/travelnews/2012/01/120112-venice-flooding-travel-science/">"Injections Could Lift Venice 12 Inches, Study Says."</a>)</p><p><em>—Ker Than</em></p>

Off the Deep End?

Floods in Venice usually mean breaking out the waders, but a few adventurous souls in St. Mark's Square threw in the towel Sunday and stripped down to swimsuits.

It's normal for Italy's "eternal city" to flood in winter, but Sunday's 5-foot (1.5-meter) inundation is the sixth highest since record-keeping began in 1872, according to the Reuters news service. (Interactive map: See how much of Venice floods at different water heights.)

"Usually flooding occurs when there is high tides and rain." Recently "strong winds from the south further enhanced the high-tide conditions," explained Shimon Wdowinski, a geophysicist at the University of Miami.

Most parts of Venice don't flood during the acqua alta ("high water"), but on Monday three-quarters of the city was underwater. As of Tuesday, the water level has begun to recede, but it may take a while, Wdowinski said. "Venice sits in a lagoon that has three outlets to the Adriatic Sea. In cases of heavy rain, like now, it takes time for the water to flow out."

A barrier to protect the city from repeated winter flooding—known as the MOSE project —is due to be finished by 2014. Until then, "there's not much that can be done," Wdowinski said. (See "Injections Could Lift Venice 12 Inches, Study Says.")

—Ker Than

Photograph by Luigi Costantini, Associated Press

Pictures: Venice Flood Makes a Swimming Pool of St. Mark's

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