RIO DE JANEIRO—The throngs streaming into Rio for a sustainable development conference may be dreaming of white-sand beaches and clear, blue waters, but what they are first likely to notice as they leave the airport is not the salty tang of ocean in the breeze, but the stench of raw sewage.

That's because the airport sits by a bay that absorbs about 1.2 billion litres of raw waste water a day: 480 Olympic swimming pools worth of filth.

As they head into the city, they will note soda bottles bobbing on the water and the colourful detritus that wreathes the shore: discarded television sets, couches and broken toys snarled in plastic. They will likely get caught in a traffic jam, peering out at the acrid haze of diesel fumes and exhaust from the commercial port that lingers over the city.

The United Nations Environment Program warned this month that the planet's environmental systems “are being pushed towards their biophysical limits,” and for the 50,000 visitors from 190 countries streaming in for the UN Conference on Sustainable Development, the welcome here is a rank reminder of just how hard it will be to balance economic growth and environmental protection elsewhere across the globe.

“Rio, the host city, has a range of urban problems: air and water pollution, social exclusion, water supply,” said Carlos Bocuhy, who heads the Brazilian Institute of Environmental Protection. “But what we have here is a crisis in a civilizational model. We are nearing a moment when all these crises will start feeding into each other. We are facing the possibility of collapse if we don't change course.”

The problems visitors will see in Rio alone are daunting. Take the bay. Twenty years ago, when the last UN Earth Summit was held here, promises were made to clean it up. Since then, seven waste treatment stations have been built, but due to poor planning and corruption, only three of them work, and at a fraction of capacity.

Even on Governor's Island, which houses both the international airport and the federal university of Rio de Janeiro, waste water pours unfiltered into the environment. The treatment plant there doesn't work either, said Sandra Azevedo, a biologist with the Carlos Chagas Filho Biophysics Institute.

“We are living here in a time and space warp. We have problems like, 'My Wi-Fi is down,' 'I'm stuck on this problem in my stem-cell research,' and at the same time, we are right next to open, running sewage,” she said. A five-minute walk separates Azevedo's office from the bay's shore.

“We work next to a massive toilet,” said Azevedo. “There is no recycling. It's not acceptable.”

Many of Rio's poorest residents still count on the bay, polluted as it is, for food. Even as Azevedo complained about the bay, Severino Raimundo Batista was getting his boat ready for a few hours of fishing.

Tourists who catch a glimpse of the bay will often see several of Batista's neighbours in the nearby shantytown throwing a net, hoping to catch something for dinner, he said.

“It used to be much better, the catch here,” he said. “Recently, it's been very dirty, a lot of trash floating.”

The Inter-American Development Bank and the state are funding a $553 million cleanup project meant to dredge canals, build new sewage plants and restore marshlands.

Batista is waiting for the day it's finished.

“This used to be good for fishing,” he said. “It was a beauty. It would be good to see it like that again.”

The 50-kilometre taxi ride from the airport to the Rio Centro convention centre offers visitors a cityscape that could double as a to-do list of issues to be tackled.

To the side of the highway, you can often see children playing in the dirty canals that run below unfinished brick buildings clinging to vertiginously steep hillsides. That's the shantytown of Manguinhos. When it rains, homes like those run the risk of collapsing. Last year, more than 900 people died when torrential rains caused mudslides and tore down similarly fragile housing in the mountains north of the state.

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The taxi slows down in a sea of red brake lights. The topographical features that make Rio so pretty to visitors — the mountains, lakes and rivers — also make it difficult to lay down a straight road. Add to that a 40 per cent hike in the number of cars over the last decade, and you've got an idling, polluting transit mess.

“It's much worse now,” said Mauricio Pinto Gama, a taxi driver who has been working Rio's streets for 14 years. “Before, you knew what the rush hour was. Now you don't. It can be bad at any time. You never know how long it'll take.”

That traffic is one reason the level of Rio's air pollution index is triple what the World Health Organization considers acceptable.

In preparation for the World Cup and the Olympics, Rio is laying down new thoroughfares connecting the far ends of town. But the transportation along these corridors will be by buses — newer, cleaner ones, but still, fossil-fuel burning hulks.

At the convention centre, the contrast of extremes that mark this city repeats itself. Rio Centro is set against a stunning backdrop of soaring granite mountains topped by lush forests. It is surrounded by marshland that sparkles with interconnected coastal lakes. Nearby is a vast beach whose white sands go on for miles.

On closer inspection, this landscape also reveals how much it has been abused. Trash and sewage accumulated over the years choke channels that let water flow between the lakes and the ocean. Pigs root through islands of clotted refuse just hundreds of meters from where world leaders will nail down shared goals on topics like ocean acidity and biodiversity.

A heritage of poor infrastructure dating back to when Brazil was a Portuguese colony, coupled with untrammeled development in recent decades and negligible monitoring, has left many of the communities surrounding the convention centre without a connection to wastewater treatment centres. That is as true for the expensive high-rises in gated communities that have sprouted on the marshy fields as for the low-income squatter communities housing the maids, doormen and landscapers who work there.

Occasionally, cyanobacteria blooms, coating the lakes with a vivid green film that produces toxins that can sicken even in small doses, said the biologist Azevedo.

“Twenty years ago, these lakes were nurseries, places where fish reproduced,” said Azevedo. “Now you have places with zero oxygen, with a pH of 0 or 1, very acidic.”

The pollution spread via channels, including one that travels right through the heart of the convention centre, where the visitors will sun themselves on grass beside waste water.

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