I was in Venice in Oct 2020. I knew there was a flood defence system to prevent the waters from the lagoon overflowing into the city. It had been tested for the first time in July 2020, after a long delay. Large yellow gates are situated in 3 places at the entrance to the lagoon (image from Guardian)
The gates were tested again in early Oct, just before my visit. So I was surprised to read there was a big flood in Venice just 2 months after my visit, on 8 Dec. It seems the gates need 48 hour to be activated and the authorities were caught off guard. The weather forecast had been inaccurate.
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UPDATE, THOUGH NOT DIRECTLY RELATED TO FLOODS
March 2021
Venice bans cruise ships from historic centre
Italian authorities have approved a ban on cruise ships entering the historic centre of Venice.
The country's culture minister said that the decision came in response to a request from UN cultural body Unesco.
Large ships will now have to dock at the city's industrial port until a permanent solution is found.
Critics argue the ships cause pollution and erode the foundations of the city, which suffers from regular flooding.
Italian ministers agreed that large cruise and container ships would no longer be able to enter the city's Giudecca canal, which leads to the historic St Mark's Square.
Photos from BBC article -