Tourists attached plastic bags to their legs or stripped off to take a dip in St Mark's Square in Venice on Sunday as rising sea waters surged through the lagoon city. High water measuring 1.49 metres (5ft) above the normal level of the Adriatic sea came with bad weather that swept Italy at the weekend, causing floods in historic cities including Vicenza as well in the region of Tuscany 250 miles further south.

Venice's high water, or "acqua alta", said to be the sixth highest since 1872, flooded 70% of the city and was high enough to make raised wooden platforms for pedestrians float away. The record high water in Venice – 1.94 metres in 1966 – prompted many residents to abandon the city for new lives on the mainland.

Venetians bombarded Facebook with moans about the city's weather forecasters, who had predicted just 1.2 metres of water on Saturday, before correcting their forecast at dawn on Sunday.

"How come the people from the council who put out the wooden platforms were predicting 150cm?" asked Matelda Bottoni, who manages a jewellery design shop off St Mark's Square, which floods when water reaches 105cm. "Many residents and shopkeepers had gone to the mountains for the day and did not have time to rush back."

Bottoni is so used to floods she has installed waterproof furniture and an angled floor. "I cannot keep the water out, but at least I can make sure it goes straight back out when it recedes," she said.

Matteo Secchi, a hotelier and head of a protest group, who grew up in ground floor flat in Venice and recalls splashing into water on getting out of bed, said his hotel was only safe up to 140cm. "This morning the lagoon came right into the hotel entrance, and this is not clean water – you need to mop with disinfectant twice after it goes down," he said. "The British tourists don't complain but the Americans can't understand how it's possible."

Secchi complained that a running event around the city had not been cancelled on Sunday. "As Venetians were trying to fix their homes and shops, people were running down the flooded streets splashing everyone with water," he said.

Alessandro Maggioni, the city's assessor for public works, defended the Venice weather centre, describing the high water as "exceptional and unpredictable". The Moses flood barrier system being built to protect the lagoon, due for completion in 2015, would have kept the city dry, he said. "Meanwhile, there is no rise in the incidence of high waters," he said.

Bottoni disagreed. "My shop now has some form of flooding 100 days a year, up from 30-40 days when I moved in just 10 years ago." But she does not plan to leave. "I was born and raised here and will stay here for the satisfaction of being in Venice."