The famous Maracana stadium in Rio de Janeiro will host soccer matches at the 2016 Olympic Games. Picture: Yazeed Kamaldien

Rio de Janeiro - From the glorious Maracana stadium to a sewage-filled bay, a huge variety of settings will greet athletes and sports fans at the Rio Olympics next month.

This is the first time a South American city has hosted the Summer Games, and the challenge has been made all the harder for Brazil since the economy skidded into deep recession.

The good news is that all stadiums and arenas have been declared complete, barring the odd cosmetic tweak. The main concern is whether a revamped transport network will be ready for the August 5 opening ceremony.

Brazil's most iconic city has been split into four hubs for the Games.

The main complex is the Olympic Park in the well-off western Barra da Tijuca area, which notably will have the tennis, most swimming, gymnastics, judo and wrestling events.

Deodoro, a modest neighbourhood in the northwest of Rio that doesn't usually see many tourists, will host competitions including equestrian events, field hockey, rugby sevens and canoeing.

Neighbourhoods at or near the famous Copacabana beach in southern Rio will host sailing, rowing, long-distance swimming events and beach volleyball.

Some of the most glamorous events - the opening and closing ceremonies and athletics competitions - will take place in two northern football stadiums: the beloved Maracana and the Joao Havelange stadium, now renamed the Olympic Stadium.

The football tournament will be spread around the country at former 2014 World Cup sites, before final rounds play out in Rio at the Maracana and Olympic stadiums.

Sailing and windsurfing will be based at Marina da Gloria, near Copacabana, with the courses out in Guanabara Bay. Aquatic marathon and triathlon swimming will take place off Copacabana beach.

But decades of pollution have put the beautiful Guanabara Bay in danger of ecological ruin and there are fears for the health of athletes.

Authorities had promised a huge cleanup, with reform of the city's sanitation system so that at least 80 percent of sewage reaching the sea would be treated. That goal was abandoned and ecologists say that currently no more than 50 percent of sewage is treated.

Guanabara Bay also sees vast amounts of floating garbage, such as plastic bags and bottles. Trash-collecting boats will encircle the sailing courses to try to prevent anything getting in the way of the speeding boats.

Reports of oil spills, a drug-resistant superbug, and even a human arm reportedly found floating in Guanabara in February have added to worries. But on television at least, the sailing events will be among the most photogenic of the Games.

Rio de Janeiro is a sprawling place divided by steep hills, favelas and traffic-clogged roads, so transport can be challenging.

Organizers hope to have solved that problem with a new metro line and an express bus system called the BRT that they say will zip between the four sporting hubs.

But the city is on tenterhooks over whether the metro extension - the biggest infrastructure project in the city - will be ready. It's only due to open four days before the opening ceremony, which is practically last-minute in terms of a such a vast undertaking.

Even if it does open, use will be restricted to people with Olympic event tickets. The general population will only be able to use the new metro after the Games.