The Rodrigo de Freitas lake, which was largely cleaned up in recent years, was thought to be safe for Olympic rowers and canoeists. But an investigation by The Associated Press found it to be among the most polluted sites. Leo Correa/AP hide caption

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Rio has hosted competitions that include athletes with physical impairments (above: the open water swim at Copacobana beach for the Rei e Rainha do Mar). But there's never been an event on the scale of the Paralympics. Buda Mendes/Getty Images hide caption

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Performers from the Beija-Flor samba school parade on a float during Carnival celebrations at the Sambadrome in Rio de Janeiro on March 3, 2014. That year, the Beija-Flor parade was centered on a theme of communication throughout history; this year's theme, underwritten by Equatorial Guinea, is more controversial. Felipe Dana/AP hide caption

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An officer from Brazilian Police Special Forces took aim Tuesday during the violent protest that broke out in one of Rio de Janeiro's slums. People there blame police for a young man's death, and say authorities are clamping down too hard in advance of this June's World Cup soccer tournament and the 2016 Summer Olympics, both of which will be held in Brazil. Christophe Simon /AFP/Getty Images hide caption

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Hundreds of thousands of people crowd Copacabana Beach in Rio de Janeiro on Sunday as Pope Francis celebrates the final Mass of his visit to Brazil. Security lapses, traffic chaos and other logistical snafus marred the visit. AFP/Getty Images hide caption

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A demonstrator is shot by a rubber bullet as anti-riot police officers charge during a protest Thursday against corruption and price hikes in Rio de Janeiro. Christophe Simon /AFP/Getty Images hide caption

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