High tide floods Venice (PHOTOS)

A man walks on the flooded Saint Mark's square during an "acqua alta" ('high waters') flooding.(AFP Photo / Olivier Morin)
Water levels rose to critical levels overnight in Venice, as a high tide forced tourists to wait it out in knee-deep water. The city was put on high alert as water was not expected to recede for at least 15 hours.

Over half the city was flooded, with water reaching above 140cm, making it the highest tide since December 2010.

Chioggia, a town on the southern edge of the Venice lagoon, was the worst hit, with water levels reaching 160cm.

The flood was caused by wind and rain combined with periodic tidal phenomenon unique to the region, AFP reported.

Venice was built on hundreds of small islands and often experiences high water levels in autumn and winter.

Venice usually starts flooding when water levels reach 110cm, then when the levels rise beyond 140cms, 58 per cent of the city goes underwater.

Italian authorities are aware of the problem and have begun to build a dam system, the MOSE, which will prevent the water levels to go beyond 110cm.

The dam costs US$7.9 billion and is scheduled for completion in 2014. However, recent austerity measures in Italy are making this hefty price tag burdensome.

Reuters / Stringer Italy
Reuters / Stringer Italy
Reuters / Stringer Italy
Reuters / Stringer Italy
AFP Photo / Olivier Morin
AFP Photo / Olivier Morin

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AFP Photo / Olivier Morin
AFP Photo / Olivier Morin

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AFP Photo / Olivier Morin
AFP Photo / Olivier Morin

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AFP Photo / Olivier Morin
AFP Photo / Olivier Morin