For a popular tourist destination like Venice, it’s best to avoid the peak season, which falls in summer (from June to August). During those months, the population of Venice almost doubles and it becomes too crowded to explore the historical area without being overwhelmed. The lethal combination of high temperatures (27-30°C) and high humidity can be oppressive, particularly so in crowded streets.
Winter time in Venice can be rather cold, with temperatures dipping to -1°C in the evenings. Flooding also occurs quite often in November and December, so pack a pair of rain boots for acqua alta (high water). During low season in January and February, some restaurants and hotels will often close, though most of the museums and other tourist destinations remain open.
The best time to visit Venice is in spring (April to May) and fall (September to October) when temperatures are pleasant at around 18 to 22°C. It’s not as crowded and hotel rates are still not too high.
The Carnival of Venice (Carnevale di Venezia) is the biggest festival held in Venice, and it’s a great time to witness locals dressed in Victorian costumes and elaborate masks. The Carnival takes place on Shrove Tuesday (Mardi Gras), usually sometime in February or March. Another major event is the Historical Regatta (“Regata Storica”), a boating competition that takes place along the Grand Canal every September.