From UNESCO, 2011.01.23. Bolds are mine:
UNESCO has called on the Italian government to restrict access of large cruise ships to culturally and ecologically important areas, particularly Venice and its Lagoon which are visited by some 300 large cruise ships a year.
In a letter sent to the Italian Environment Minister on behalf of Director-General Irina Bokova, the Assistant Director-General for Culture Francesco Bandarin writes that “the tragic accident [of the Costa Concordia on 13 January] reinforces longstanding concern over the risk that large cruise liners pose to sites inscribed on UNESCO’s World Heritage List, particularly the Venice Lagoon and the Basin of San Marco.”
After presenting UNESCO’s condolences for the tragic loss of life caused by Costa Concordia accident and praising the efforts of the rescue teams and local population in dealing with the disaster, the letter urges the government to act quickly to develop alternative plans for maritime traffic around the World Heritage site of Venice.
The cruise liner traffic in Venice is particularly damaging because of the fragile structure of the city. The ships cause water tides that erode the foundations of buildings. They contribute to pollution and impact the cityscape as they dwarf monuments in the heart of the city.