If you’re heading to Venice on holiday this summer, don’t forget to pack your pollution mask. Worrying about toxic air might seem strange in a city with few roads and cars, but Venice’s air carries hidden risks.

Every day five or six of the world’s largest cruise ships chug into the heart of the ancient city, which hosts the Mediterranean’s largest cruise terminal. These ships advertise luxurious restaurants, vast swimming pools and exotic entertainment – but keep quiet about the hidden fumes they pump into the city’s air.

It’s one reason locals are so enraged over the impact of tourism on their famous city. Protests against cruise ships are commonplace. In May nearly 20,000 Venetians voted in an unofficial referendum, with 99% backing a motion to keep cruise ships away.

They are right to be angry.

Ship operators claim they use low-emission fuel when they are near big cities, but measurements I have taken near the port of Venice tell a different story. The fuel they burn while at berth contains more than 100 times as much sulphur as truck diesel.

As big ships sailed down the main canal, just a stone’s throw from the shore, my team recorded up to 500 ultra-fine particles per cubic centimetre – 500 times higher than clean sea air.

These particles linger in the air long after the ships have passed, and are carried hundreds of kilometres inland by the winds. Particulate matter is linked to severe health problems such as cardiovascular and respiratory diseases, including strokes and cancer.

The World Health Organization places diesel particles in the same carcinogenic category as smoking and asbestos.

And it’s not just particulates we should worry about. The dieselgate scandal has reminded us that diesel engines produce a range of other pollutants that damage human health, the environment and the climate, including carcinogenic soot and sulphur and nitrogen oxides.

Figures by the European commission estimate that about 50,000 people die prematurely every year in Europe because of pollution from the shipping sector. This is a scandal because there are measures available to fix the problem cost-effectively, from using cleaner fuels to installing filters and using battery technology near the coast.

But the very profitable cruise industry has proven unwilling to engage with the problem. Nearly a million Britons take a cruise holiday every year, many paying up to £1,000 each for a week-long trip around the Mediterranean. With more than 6,000 passengers packing the larger ships, that’s a decent revenue.

Despite this, major shipping lines still refuse to spend money on proper exhaust gas technology, creating a massive threat to the health, not only of citizens and guests of the ports they visit, but of citizens along the coasts and even inland.

The fumes can also endanger the passengers: the German lung doctors association recently gave a warning to passengers with pre-existing conditions not to go on the deck of a cruise vessel. Even newer ships still pump out incredible levels of pollution.

The cruise industry is failing to meet basic public standards on the environment and human health. The good news for Venetians is that the Port Authority expects 10% fewer vessels this year, which may allow residents to breathe slightly easier.

But until ships are fitted with better filters and burn cleaner fuel, I’d advise you to pack a mask for when they sail by.