Venice becomes the first city in the world on Thursday to introduce a payment system for tourists in an effort to thin the crowds that throng the canals during the peak holiday season.

Any visitor who is not staying the night must pay a 5 euro ($5.35) entry fee online before walking into the lagoon city on April 25 - a national holiday and the first of 29 days this year when visitors are being charged to get in.

Although there are no turnstiles at the city gateways to make sure people have a pass, inspectors will be making random checks and issue fines of between 50 and 300 euros to anyone who has failed to register.

“No one has ever done this before,” Venice Mayor Luigi Brugnaro told reporters earlier this month. “We are not closing the city … we are just trying to make it liveable.”

Some 20 million people visited Venice last year, a city official said, with roughly half of them staying overnight in hotels or holiday lets - an influx which dwarves the resident population currently put at around 49,000.

Venice narrowly escaped being placed on UNESCO’s “World Heritage in Danger” list last year partly because the U.N. body decided that the city was addressing concerns that its delicate ecosystem risked being overwhelmed by mass tourism.

Besides introducing the entry charge, the city has also banned large cruise ships from sailing into the Venetian lagoon and has announced new limits on the size of tourist groups.

“The phenomenon of mass tourism poses a challenge for all Europe’s tourist cities,” said Simone Venturini, who is responsible for tourism and social cohesion on the city council.

“But being smaller and more fragile, it is even more impacted by this phenomenon and is therefore taking action earlier than others to try to find solutions,” he told Reuters.

Ticketing this year is in an experimental phase and Venturini said that in future Venice might start charging more at certain times of the year to look to discourage arrivals.