Protesters dressed as clowns marched through the capital and other cities across the country as government-led ceremonies marked Brazil's independence from Portugal in 1822. Organizers chose the occasion to point to the huge challenge posed by endemic corruption that they said threatens to tarnish Brazil's image as a vibrant, emergent regional power.
Political corruption has bedeviled successive democratic regimes since the end of the 1964-85 military rule but, until Rousseff launched a clean-up, it was tolerated by legislators, politicians and the media as part of the scene. With all sides harboring sensitive, often incriminating, information about each other it was difficult for any anti-corruption drive to make headway.
Rousseff set out to change that through internal investigations and disciplinary measures that originally began as discreet acts. The country's popular press latched on to the story with great gusto and soon one embarrassing revelation led to the next, forcing high-profile resignations in the government and congress.
Four government ministers and several members of the National Congress have left over corruption allegations since Rousseff took office in January.
Dozens of government officials have also lost their jobs or been arrested on various charges of malfeasance, while media revelations continue to target other key officials, including several other ministers. All have all denied wrongdoing.
The mood in the protests was mixed. Many of the demonstrators chanted slogans in support of Rousseff's anti-corruption program while others showed their frustration over continuing social problems seen behind corruption. In Brasilia, protesters said they had no political affiliation, countering suggestions the marches could be part of an opposition plan to disorient the president in her first year in office.
The drive against corruption has left many of those affected, their friends and relatives angry with Rousseff. Critics said the campaign was at risk of becoming a witch-hunt that could take the innocent or those wrongly accused in its populist sweep.
"Corruption in our country is a pandemic that threatens the credibility of institutions and the entire democratic system," a statement jointly issued by the College of Lawyers, the Brazilian Press Association and the National Bishops' Conference said.
Rousseff's chief of staff Antonio Palocci was among those who resigned after media reports in June questioned his wealth, seen to be disproportionate to his means. After Palocci's departure the ministers of defense, agriculture and transport also quit following media allegations, though all of them denied wrongdoing.
The campaign, while widely welcomed, has had the unexpected outcome of threatening Rousseff's fragile coalition with other political parties that lost their ministers in the cabinet. Rousseff belongs to the Workers Party, like her predecessor Luiz Inacio Lula da Silva. Lula's huge public approval ratings helped him survive several corruption scandals during his presidency from 2003-10.
The anti-corruption campaign has eclipsed the government's other major endeavor, to clear Brazilian cities of sprawling shanty towns. The favelas are hotbeds of organized crime gangs. The largest of them, the Alemao Complex in Rio do Janeiro, fell back under the control of criminal gangs within days of its "pacification" by military forces.
Brazil is keen to brush up its urban image before it hosts the 2014 FIFA World Cup and the 2016 Olympic Games.