The Phenomenon of Acqua Alta – High Water in Venice

by Elena Binda
The high water in Piazza San Marco (c) Shutterstock.com

We’ve all been enchanted by photos of St Mark’s Square emerging from the water. Here is an explanation of what causes this, and how to deal with a phenomenon that reaches its peak annually in November to the joy of Instagrammers but not so much for the locals.

What is the Acqua Alta?

The phenomenon of Acqua Alta (c) Shutterstock.com

Acqua alta days usually occur in autumn, peaking in November, and are known as ‘acqua alta’ days. During these days, Venice is partially submerged for a couple of hours, the time needed for the water to flow back into the sea. Most of the time ‘acqua alta’ is only a mild nuisance, involving a few centimeters, or in some cases, about ten centimeters of salty water – nothing that can’t be overcome with a sturdy pair of rain boots. So, relax and enjoy the situation.

Why does it happen and where?

The high water forecast in Venice

‘Acqua alta’ happens when strong southeasterly winds, like the Scirocco, blow over Venice. When they reach speeds of over 25km/h the winds force the water in the Adriatic sea into the Lagoon.
When this happens, the shallow basin of the lagoon is flooded with more water than it can contain, causing the water to rise and flood the streets and squares of Venice. The most severe flooding occurs when a high tide, caused by the moon’s gravitational pull, or the swollen waters of the Adige and Po rivers – both of which are tributaries of the Adriatic Sea – coincide with these weather conditions. A combination of all three factors, more likely during the rainy autumn months, gives rise to the ‘perfect storm’. High waters can register peaks ranging from 110 centimeters upwards. However, take note: this measurement only refers to an increase in altitude with respect to the average sea level, and does not indicate the height actually experienced by pedestrians. For example, a high tide of +100 means that there are only likely to be a few puddles. Furthermore, the streets of the city are located at different levels, meaning that even during exceptionally high tides not all parts of Venice are affected. Flooding can vary from a few millimeters in the city’s innermost ‘calli’, to more than half a meter in St. Mark’s Square, the lowest part of the town.

Tourists and Acqua Alta: time for epic shots!

Tourists taking selfies on High Water (c) Antonio Gravante/Shutterstock.com
Tourists taking selfies on High Water (c) Antonio Gravante/Shutterstock.com

From an aesthetic and practical point of view, the effect is remarkable. Tourists usually love this phenomenon because it creates a fantastical, slightly surreal, unique and extraordinarily photogenic landscape. The city is filled with Gene Kelly ‘singing in the rain’ wannabes, intent on posing (and posting), whilst sending up sprays of water amongst window displays and lamp posts. The chairs and tables of bars appear to float as if suspended; the reflections of majestic facades are doubled, in short, it’s an instagrammer’s paradise! Arm yourself with a smartphone or a camera. When the tide retreats, small pools of water remain in St. Mark’s Square, and in the ‘calli’ and, it is here, for the rest of the day, that that glorious Venice is reflected in all of its beauty.

How do locals perceive this phenomenon?

The walkways in san Marco

Venetians, born and bred, living and working in the city year-round, are not as enamoured of the ‘acqua alta’ as the tourists. Although this phenomenon is not a danger to humans, it causes a number of disruptions; hindering traffic, flooding cellars and warehouses and damaging objects. The problem mainly affects shops in the centre because they are situated at the lowest point in the city so this area is most prone to flooding even when the tide is not particularly high. As a result, shops in and around St. Mark’s Square are often equipped with waterproof bulkheads, designed to protect their interiors, in the event of flooding.

How to behave

A calle and one of Venice's bridges during the acqua alta
A calle and one of Venice's bridges during the acqua alta

The city’s administration has implemented various measures to deal with it. When there’s a sea level forecast of +110 centimeters, the population is alerted by warning signals. At the same time, the city provides elevated wooden walkways in areas that are prone to flooding.
Vaporetti continue working, although some lines may be subject to change. In any case, access to most of the town is guaranteed. In the event of an exceptionally high tide, generally starting from about 120 centimeters, you’ll need to wear a pair of rubber boots to get around the city. Though picturesque, walking around barefoot is not advisable.
Remember that, even under these conditions, it’s necessary to respect the city. Both tide forecasts and a list of prohibitions and sanctions can be found on www.comune.venezia.it (in Italian only).

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