Tourists stroll the city in boots or on boardwalks among seagulls swimming around them. If feeding pidgeons is popular on a regular day, feeding seagulls is fun during high tides. Flooding causes major structural damage to the foundations and the buildings in Venice. Tides carry away soil from the bottom and cause Venice to sink even faster in some places. Buildings are therefore structurally instable and several reconstruction works are underway. The city is sinking one to two milimeters a year, while the north lagoon is subsiding 2 to 3 mm a year and the islands in the south lagoon are sinking at a rate of 3 to 4 mm a year. This subsidence will have to be accounted for by the scientists trying to protect the lagoon.