Venice floods most often in October, November and December, when a high astronomical tide meets a storm surge pushed up the Adriatic and the water reaches the pavements. That is acqua alta. The season runs from October to March, and about 75% of events fall in those three months (Comune di Venezia, 2009). Water covers the lowest ground first, starting with Piazza San Marco.
Tide heights in Venice are quoted against the Punta della Salute datum (ZMPS), the local mean sea level of 1897. Flooding in Piazza San Marco begins above 80 cm on that scale, and the lowest point in the city, the ground in front of the Basilica entrance, sits at about 63 cm (Comune di Venezia, 2009; ISPRA, 2025). Since the MOSE gates entered service the picture has changed: the barriers are raised when the forecast points to a tide above 110 cm, and in 2025 the historic centre recorded no tide at or above that level at all, against 7 measured out at sea (Autorità per la Laguna di Venezia, 2026; ISPRA, 2026).
For a visitor this means a soaking is now unlikely, and an inconvenient morning is still possible. This page sets out when acqua alta happens, how often, what the numbers on a forecast mean, what MOSE does and does not stop, and how to plan a day around a high tide.
When is acqua alta in Venice in 2026?
The season is autumn and winter. Storm surges driven by sirocco winds up the Adriatic produce a clear seasonal cycle, with the largest and most frequent events from November to March (Lionello, Barriopedro, et al., 2021). The Comune's own analysis is sharper: the peak month is November, followed by December and October, and those three months hold roughly 75% of all events. Frequency in the remaining months is very low, and no event has ever been recorded in July or August. June had never produced one until 6 June 2002, when the tide reached 121 cm (Comune di Venezia, 2009).
The last full season bears this out. MOSE was raised 49 times in 2025/2026, with logged closures running from 10 September 2025 to 15 May 2026 (Autorità per la Laguna di Venezia, 2026). ISPRA counted 26 tide maxima at or above 80 cm in November 2025, the highest month of the year, followed by March, August and October with 17 each, while February recorded none (ISPRA, 2026).
Time of day matters as much as the month. High tides in the flood season cluster in the morning, because the daily astronomical maxima fall in the morning during autumn, and no event has ever been recorded in the early afternoon (Comune di Venezia, 2009). A morning walk to San Marco is the part of the day worth checking a forecast for.
How often does Venice flood?
Two thresholds are counted. The lower one, 80 cm above the Punta della Salute datum, is the level at which water starts to cover Piazza San Marco. The higher one, 110 cm, marks a serious event (ISPRA, 2025). In 2025 there were 161 tide maxima at or above 80 cm, down from 227 in 2024, and none at all reached 110 cm inside the historic centre, though 7 were measured at sea (ISPRA, 2026).
Those totals sit on a long upward trend. Exceedances of 110 cm rose from about 4.2 per decade in the early twentieth century to 95 per decade in 2010 to 2019, and events above 120 cm went from fewer than 2 per decade to 40 in the same recent decade (Lionello et al., 2021). The driver is relative sea level rise rather than stormier weather. Mean sea level at Punta della Salute has risen at 2.6 mm per year since 1872 and at 4.6 mm per year over 1994 to 2025, and the reconstructed annual mean reached a record 41.1 cm in 2024 before falling back to 37.4 cm in 2025 (ISPRA, 2026).
The gates have broken that link for now. Between 2020 and 2024 the historic centre saw only three tides at or above 110 cm, in a period when the open sea produced many more (ISPRA, 2025).
What the tide numbers mean
Every height you will see quoted, on a forecast board or a news report, is centimetres above ZMPS, the zero of the Punta della Salute tide gauge, fixed on the mean sea level measured in 1897 (Comune di Venezia, 2009). It is a local datum, roughly 23 cm below the national reference, so a number that sounds alarming is measured from a low starting line.
A tide below 80 cm is normal and affects nothing. Between 80 and 109 cm the tide is called sostenuta: at 80 cm only about 0.1% of the public walkway surface is wet, and Piazza San Marco is most of it. At 110 cm about 14% of public walkways flood, which takes in the oldest central districts. An exceptional tide today means 140 cm or more, which puts about 55% of the walkways under water (Comune di Venezia, 2009). Older figures based on total land area rather than pavement give about 12% at 110 cm, so a guide quoting either number is describing the same event.
The extremes are rare. The record is 194 cm on 4 November 1966, which stayed above 110 cm for 22 hours, and the second highest is 189 cm on 12 November 2019 (Lionello et al., 2021). November 2019 was the worst month in the gauge record, with 15 exceedances of 110 cm and four above 140 cm.
Does the MOSE barrier stop acqua alta?
Mostly, at the levels that matter to a visitor. The mobile gates at the three lagoon inlets are raised when the forecast gives a probability of a tide above 110 cm, and they have been in operational use since the first closure on 3 October 2020 (Autorità per la Laguna di Venezia, 2026; Lionello et al., 2021). Use has climbed steeply: 20 closures in 2020/2021, 13 in 2021/2022, 19 in 2022/2023, 32 in 2023/2024, 23 in 2024/2025 and 49 in 2025/2026 (Autorità per la Laguna di Venezia, 2026).
A closure is short. In the 2025/2026 season most lasted between about three and five hours from the start of the lift to the end of ballasting, the shortest 2 hours 26 minutes on 6 October 2025 and the longest 9 hours 34 minutes on 28 January 2026. Hydraulic protection covers roughly 25 minutes less than the logged figure. Sometimes only the Lido barrier goes up rather than all three (Autorità per la Laguna di Venezia, 2026).
Two limits are worth knowing. Tides below the trigger still wet the lowest ground, so 80 to 100 cm events pass without a closure. And while the gates are up, shipping through the inlets stops, with notices issued by the harbourmaster, which can affect boats running to and from the airport and the Adriatic.
Where to check the Venice acqua alta forecast
The Comune di Venezia runs the tide forecasting and warning centre, which issues an official level forecast covering at least the next 72 hours, produced by combining statistical and hydrodynamic models with readings from a network of tide gauges in the city, across the lagoon, at the three inlets and on the CNR platform in the open sea (Comune di Venezia, 2009). Three days is enough notice to move a morning in San Marco to an afternoon.
ISPRA publishes its own modelled forecasts and live gauge readings daily for Punta della Salute, Burano, Chioggia, Malamocco, Lido, Grado and Porto Caleri, and its historic series are free to download (ISPRA, 2026). If you want a number rather than a colour code, that is the page to open on a phone.
The city also warns out loud. Warning is delivered through 15 acoustic diffusers in the historic centre, capable of voice messages, and eight electromechanical sirens on the islands and the coast (Comune di Venezia, 2009). If you hear a tone rising over the rooftops in the early morning, that is the system telling residents how high the water is expected to go. Check the current forecast level before you decide what it means for your day, because the tone alone does not tell you which streets will be wet.
What to do in Venice during acqua alta
Plan around the peak rather than the day. The tide runs on a cycle of about 12 hours and 25 minutes, with a rising and a falling phase, so the water is over the pavement for a few hours around the maximum and gone afterwards (ISPRA, 2026). MOSE closures in the last season, which cover the same window, typically ran three to five hours (Autorità per la Laguna di Venezia, 2026). Shift a San Marco morning to the afternoon and the problem usually disappears.
The city lays about 4 km of raised walkways, the passerelle, along the lowest stretches of the main pedestrian routes, which keeps the principal connections walkable during an event (Comune di Venezia, 2009). They are narrow and busy, and they follow set lines, so a detour on foot is often faster than queueing for one.
Knee-high rubber boots are the standard answer for anyone who wants to walk where the passerelle do not go. Shops near Santa Lucia station and Piazzale Roma sell them, along with foldable overshoes that pack into a bag, and prices tend to rise once a high tide is in the forecast, so buy early if you are going to buy at all. Water buses keep running through most events, though stops at the lowest landings can be moved or skipped, so check the operator's notices on the morning itself.
