Rio de Janeiro, Apr 27 (IANS): The 100-day countdown to the Rio Olympics begins Wednesday. Here's a look at the progress of preparations so far, and identifies key challenges facing organisers ahead of the opening ceremony on August 5.

Games Organisation -- Unlike the football World Cup in Brazil two years ago, the Rio Olympics have mostly escaped controversy about venue delays.

Organisers say sports facilities are 98 percent complete overall with only the velodrome running late. Problems in laying the velodrome's surface forced the cancellation of a track cycling test event last month, but Rio 2016 chief Carlos Nuzman said the venue is only a fortnight behind schedule.

The tennis centre is also only 90 percent complete although Rio officials have said it is progressing on time.

Also unlike the World Cup, there has been no public backlash towards the Olympics from Brazilians.

In a recent press release, the IOC said 70 percent of Rio residents were in favour of hosting the mega-event, showing that "local citizens see the Games as a positive element in the development of their city and country".

Despite the encouraging progress of preparations, the IOC's coordination commission warned that the most testing part of Rio's Olympic build-up was yet to come.

"The last stretch is always the hardest," commission chairwoman Nawal El Moutawakel said earlier after the body's final pre-Games visit to the city earlier this month.

Political crisis, Recession -- Brazil's lower house last week voted to impeach President Dilma Rousseff for her alleged manipulation of government accounts. The motion against her has now been passed to the senate, which could decide in favour of an investigation into the claims as early as next month.

That would force Rousseff to step aside for at least 180 days, raising the prospect that her deputy, Michel Temer, will lead the government during the Olympics.

The beginnings of the crisis were evident during the lead up to the 2014 Football World Cup, when millions of Brazilians marched through major cities to protest against stadium costs, corruption and shoddy public services.

City Infrastructure -- While most of Rio's Olympic sports venues are on track to be completed on time, there have been concerns about delays to new transport links, particularly a new subway line connecting the city to Olympic Park in Barra da Tijuca.

Hundreds of engineers and labourers are working round-the-clock to complete the project before its July 1 deadline.

According to the government, the line will transport more than 3,00,000 people a day and greatly reduce traffic congestion in the city's south and west.

Infrastructure concerns heightened last week when an elevated bicycle track collapsed into the sea, killing at least two people.

Security -- The government has said it will deploy some 38,000 armed forces during the Games, backed up by 48,000 police and firefighters. The security operation is about twice the size of that used for the London Games in 2012.

Despite a commitment to ensuring the safety of athletes, officials and tourists, the government last month cut its Olympic security budget by $550 million.

Officials said the move would mainly impact investments that are not directly related to the Games, such as an urban pacification unit within the Mare shanty town complex in Rio's north.

Pollution -- Earlier this month IOC chief Thomas Bach guaranteed the Games would be safe for sailing events despite concerns about water quality in Rio's Guanabara Bay.

The Rio government has admitted it won't be able to meet a 2009 pledge to reduce pollution in the bay by 80% ahead of the Games.

But officials say a vast network of nets, known as eco-barriers, have been strategically placed to prevent rubbish and waste entering the bay.

Concerns have also been raised about water quality at the Rodrigo de Freitas lake, which will host rowing and canoeing events. The government said a cleanup operation of the lake had ensured it will meet international standards for the events.

Legacy -- As part of Rio's Olympic legacy pledge, many venues built for the Games will be turned into public schools, sports facilities and leisure centres.

Organisers say the Games will improve the quality of life for Rio's citizens through infrastructure works like new public transport links and better waste management.

In addition, thousands of people will benefit from job training, creating pathways for new careers.