The mayor's year-old, zero-tolerance campaign against petty crimes and disorder is on full display at the first Carnival since Rio won its bid to host the 2016 Olympics.
Those who drink too much beer at giant street parties and want to use gutters as toilets - always tolerated in the past - are out of luck. Police have already arrested nearly 100 such lawbreakers.
Beaches no longer resemble full-service bazaars with greasy snacks delivered on command under a sprawl of rented umbrellas.
Beach football by the sea? After 5 p.m. only please.
And something else is missing. Rio's world-famous waterfront pickup club for legal prostitutes has closed to make way for a museum.
The changes were getting mixed reviews even before the party officially started.
"The plan is doing the impossible: making Rio square," said Marcus Paulo Reis, a 36-year-old businessman sipping beer at lunch this week in the beachside Arpoador neighbourhood. "They're trying to get rid of the grit that gives Rio its flavour."
Violence is still the city's biggest security concern, with at least seven suspected drug traffickers and a policeman killed Thursday in a shootout in a slum in northern Rio.
There appears to be a silent majority glad to get some peace on the beach and during this week's party, as international headliners poured into Rio, including Madonna, Beyonce, Alicia Keys and Paris Hilton.
"It will make Carnival more secure," said Alexandre Verissima, a 34-year-old actor, standing on Ipanema beach in only his blue Speedo.
To prove his point, he acted out a scene on a nearby, unsuspecting French tourist.
"In years past, you would see this happen right here," Verissima said, lunging toward the tourist's backpack and acting like he was going to run off with it, not to the amusement of the visitor. "You see, this does not happen anymore."
Amid the law-and-order makeover, a 7-year-old girl was preparing to samba before a crowd of thousands as a Carnival drum corps queen, a coveted role normally reserved for sultry models. A family court judge overruled objections that it is inappropriate for little Julia Lira to be in such a traditionally sexualized role.
Much like New York City's government did in the 1990s, Mayor Eduardo Paes wants to end Rio's general lawlessness with a zero-tolerance campaign he calls "shock of order."
The headlines have come nonstop for a year: Shock of order on the beaches. Shock of order on public transportation. Shock of order on illegal billboards.
As he handed the key to the city over to the Carnival King Momo - who rules the city until Ash Wednesday - Paes made it clear who really was in charge. He stood before journalists holding a sign underscoring his anti-urine campaign that read "Come on, don't pee here, OK?"
Annatolio Isidoro, a dapper 77-year-old dressed in a tan, linen suit and straw bowler hat who serves as the official "Samba Citizen," said the rules would only make Carnival better.
"We've long needed some organization to better show off our great party to the entire world," he said while attending the hand-over ceremony.
But the effort has left a bad taste in the mouths of some Cariocas, as Rio residents call themselves, especially those who make their living on the beach - the destination for up to 2 million people on a hot summer day.
Beloved beach vendors who once operated out of hand-painted tents - providing chairs, sun umbrellas, drinks and food - are now forced to use the same model of tent and rent just 100 chairs and 30 umbrellas each, all with no markings.
This has disoriented the hordes who tend to go to the same beach spot each weekend their entire lives. Like staring into Brazil's brilliant sun too long, looking at row after row of indistinguishable, white tents has Cariocas furiously using their cellphones, trying to locate friends and family.
"I've lost so much money since they started this garbage," said vendor Jonildo Viegas da Silva, known by his clientele as Nildo. "No more selling fruit salad, no more sandwiches. I'm losing customers because I run out of chairs to rent by 10 a.m."
Nildo said last Carnival he made about $5,400. This year, based on how business has been under the new regime, he is hoping for half that.
"I've got 12 men who work for me here, and they all have families," he said. "We've got to divide what little we'll have and hope it sustains our wife and kids."
Eager to clean up the beaches, the mayor has outlawed food like fried shrimp and grilled cheese sticks that have soaked up booze in Brazilian bellies for generations. Beer and drinks are still served in the 100-plus degree (38 Celsius) heat forecast for Carnival.
Citizens who long turned beach sidewalks into weekend parking lots are being hit with fines. Even that most sacred of Brazilian pastimes - beach football - is targeted. No more kicking the ball near the water until 5 p.m.
One of the city's toughest challenges - and biggest victories - was closing down a notorious disco where hundreds of prostitutes would gather each night to meet up with an almost exclusively foreign clientele.
The fact that the Help Disco was located at the heart of Copacabana beach long embarrassed officials.
Last month, it closed. In its place, a museum dedicated to Brazilian music, film and photography will be erected, to the dismay of some Carnival revelers.
"It's heartbreaking," said Brian, a 46-year-old American tourist, motioning toward the dark building which just a few weeks ago would have been lit up like a samba group's float. He would only give his first name lest family and friends back home in Philadelphia learn of his Carnival exploits.
"I've been coming to Carnival in Rio for six years and I just found out they closed it when I got here today," he said, shaking his head. "Why couldn't they have just left it open until after Carnival?"
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