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In page Venice:

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During the 20th century, when many artesian wells were sunk into the periphery of the lagoon to draw water for local industry, Venice began to subside. It was realized that extraction of water from the aquifer was the cause. The sinking has slowed markedly since artesian wells were banned in the 1960s. However, the city is still threatened by more frequent low-level floods – the Acqua alta, that rise to a height of several centimetres over its quays – regularly following certain tides. In many old houses, staircases once used to unload goods are now flooded, rendering the former ground floor uninhabitable.[citation needed]