High water or “aqua alta” is the term used for the massive tide surges that occur periodically in the northern Adriatic Sea, which cause the flooding of the city of Venice to a smaller or a larger extent. The high-water phenomenon occurs between autumn and spring, when the high tides of huge proportions are exacerbated by the prevailing seasonal winds.
The term high water actually indicates the generic phenomenon. However, for the city of Venice, there are more rigorous definitions, based on the tide levels:
Tolerable tide - when the tide level is between +80 cm and +109 cm (defined as the average sea level measured in 1897);
High tide - when the value is between +110 cm and +139 cm;
Extraordinarily high tide - when the value reaches or exceeds +140 cm.
The high levels of water in Venice reached 190 cm in November 2019 causing enormous damage to the city of Venice. Venice has lower and higher parts of the city where, for example the area near the church “Dei Frari” gets completely flooded, as well as the main square San Marco, whereas Rialto Bridge always remains untouched as it is one of the highest points in Venice. Many luxury stores, hotels, restaurants, houses get flooded and it can take days until this damage gets sorted.
Therefore, we would advise our visitors, if they are visiting Venice in the period between the autumn and the spring to get informed whether high water is to be expected, so that they bring a pair of plastic boots with them. Visitors can also purchase plastic boots in Venice. Those are sold literally at every corner. You might get to haggle a bit about the price, as they will cost from 5 euros to 10 euros, depending on your bargaining power with the street vendors.