VENICE, Aug 9 (Reuters) - Rare summer flooding submerged Venice"s famed Piazza San Marco in up to a metre of water overnight. The lagoon city is often hit by so-called "acqua alta" (high water) in autumn and winter, and devastating floods in November 2019 caused hundreds of millions of euros of damage. A worker closes a restaurant in a flooded St. Mark"s Square during an exceptional high water in Venice, Italy August 8, 2021. Picture taken August 8, 2021. REUTERS/Manuel Silvestri People walk in a flooded St. Mark"s Square during an exceptional high water in Venice, Italy August 8, 2021. Picture taken August 8, 2021. REUTERS/Manuel Silvestri A couple dances in a flooded St. Mark"s Square during an exceptional high water in Venice, Italy August 8, 2021. Picture taken August 8, 2021. REUTERS/Manuel Silvestri 1/4 People walk in a flooded St. Mark"s Square during an exceptional high water in Venice, Italy August 8, 2021. Picture taken August 8, 2021. REUTERS/Manuel Silvestri Sunday night"s event was less damaging, however, and couples in the square danced to piano music almost knee deep in the water, while children splashed and paddled and tourists waded through, shoes in hand. Venice"s high water incidents are caused by a combination of factors exacerbated by climate change - from rising sea levels and unusually high tides to land subsidence that has caused the ground level of the city to sink. A long-delayed flood barrier was deployed for the first time last October, but it is only activated to block the most potentially damaging tides of more than 130 cm (4 ft 3 inches)and so did not enter into operation on Sunday.