Venice became 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.Signs were set up outside the train station and near an entry footbridge warning visitors they had to pay the new 5-euro ($5.35) charge before diving into Venice's narrow alleyways.April 25 is a national holiday in Italy and is the first of 29 days this year when people must buy a ticket if they want to access the lagoon city from 8.30 a.m. to 4.30 p.m.Reservations are meant to be made online but there is also a booth on hand for those who don't have smartphones."This system is very important because we are finding a new balance between the residents of the community and the day trippers," said Simone Venturini, the city councillor responsible for tourism and social cohesion.Although there are no turnstiles at the city gateways, inspectors will be making random checks and issuing fines of between 50 and 300 euros to anyone who has failed to register.However, Italian tourists arriving on Thursday said imposing another charge on visitors was unfair."I consider Venice to be the most beautiful city in the world and so to deprive a person on a low budget of the opportunity to come here for an hour or two to enjoy this city is surely a shame for these tourists," said Gabriella Pappada, from Lecce in southern Italy.The initiative is one of a series of measures in place across Italy to manage tourist flows.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 dwarfs the resident population currently put at around 49,000.People with hotel reservations and visitors aged under 14 do not need to pay the entry fee, but still need to register beforehand. Residents, students and workers are exempt.Venice narrowly escaped being placed on UNESCO's "World Heritage in Danger" list last year partly because the U.N. body decided 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.