Guanabara Bay is the major water body in Rio de Janeiro. It's a very beautiful landscape but as the city developed lots of garbage and waste water was thrown in the bay. So nowadays the water is very dirty and it's not recommended to swim there. In the Olympics it was a big problems because the athletes had to compete in the bay and some got very sick. Even though this problem have arise a long time ago, the government never really cared about it. Politicians always say that they will clean Guanabara Bay, but it never actually comes true.