We always get excited about the aerial view of Guanabara Bay. Every time we return to Rio de Janeiro through Santos Dumont Airport, we are amazed by its beauty and size. The harmonious design of the mountains makes Guanabara Bay the essence of the most beautiful postcard in the city.
Seen from above, the Bay is one of the most beautiful landscapes in the world. That is why the two main tourist attractions in Rio de Janeiro, Corcovado and Sugarloaf, together receive more than 3 million visitors every year. The main reason for this movement of people is the view, which includes – of course – Guanabara Bay.
Even so, those that govern the state and the city of Rio de Janeiro were not educated on the vital importance of decontaminating the bay. And worse, they wasted the moment before the Olympics to do that work. To imagine the dimension of pollutants, such as the oil from large vessels that are launched daily in Guanabara Bay, just look at the surrounding areas.
Guanabara Bay is home to the second largest industrial region, the second largest port in Brazil, two airports, two refineries, naval services, shipyards and an intense movement of land and sea transportation. “The Bay offers a world of services without there being a single fee that is reverted to its care,” says David Zee, an oceanographer at the State University of Rio de Janeiro (UERJ). “Nature is doing slave labor.”
Its hydrographic basin of almost 4 thousand km squared reaches areas of 15 municipalities – Rio de Janeiro, Duque de Caxias, São Gonçalo, Magé, Guapimirim, Itaboraí, Tanguá, Niterói, Nova Iguaçu, Cachoeiras de Macacu, Rio Bonito, São João de Meriti, Mosque, Nilopolis and even a small part of Petropolis. With so many actors involved, articulating common policies, such as basic sanitation itself, is a huge dilemma.
Lack of articulation, projects impossible to execute and difficulties in taking responsibility made the proposal to cleanse the Bay an entanglement of difficulties and procrastination. The biggest problem pointed out by oceanographer David Zee bumps up against a delicate issue, the favelas. The occupation of the coastal zone in a disorderly and irregular way degrades the banks of the Bay, increases the violence in the region and makes sanitation projects even more difficult.
“It is not possible to think of the decontamination of Guanabara Bay by means of basic sanitation when half of the population that throws sewage in the bay is in favelas and not in formal cities,” says Zee. “If it is already difficult to carry out this work in a normal situation, it’s almost impossible in militia-controlled locations.”
For Zee, the way out would be to place treatment units in the rivers  that empty into the bay, bringing with them tons of garbage. “But there’s another problem: who’s going to take on the job?” 
But the bay’s health has not always been so critical. In 1818, the French naturalist Joseph Paul Gaimard, who was dedicated to the discovery of new species in Rio de Janeiro, confessed to his friends that he did not like to sail through the waters of Guanabara Bay. Not because of the trash, inexistant at the time. The naturalist feared something greater! The movement of whales that swam in the region was so intense that he feared that cetaceans could sink his boat. And, until the 1950s, it was still possible to spot some whales in the bay. 
Today, the only marine mammal that inhabits the waters of Guanabara Bay is the Guiana dolphin (Sotalia guianensis) , and even so, in very small numbers. In 1985, researchers noted the presence of about 400 individuals inhabiting the bay. Today, this group would be no more than 34. The latest victim, known to researchers as Acerola, was found dead by Comlurb officials on June 15, 2016. At UERJ, which maintains the Laboratory of Aquatic Mammals and Bioindicators (MAQUA), Professor Izabel Gurgel nicknamed this group, which declines annually in size, as the “heroes of resistance.”
According to Maqua researchers, the boto (river dolphin) happens to live in the same place where it is born. The researchers identified that the boto uses an echolocation strategy that allows the animal to detect objects that are at sea. The ability to recognize locations and detect danger allows the species to continue to exist in impacted environments. In this way, porpoises can choose a less polluted place to survive. This is the case of the dolphins that live in the 20 km squared area of the Guanabara Ecological Station, which, next to the APA Guapimirim, is one of the few places where fishing nets are not allowed and there are few humans.
Maqua researchers also identified the death of green turtles in Guanabara Bay. Garbage, chemical pollution and trampling by boats are the main causes of the disappearance of the turtles that dare to venture through the waters of Rio de Janeiro. The species is also considered to be endangered by the International Union for Conservation of Nature (IUCN).
Measuring up to 1 meter in length and weighing almost 200 kilos, the green sea turtles (Chelonia mydas) come from afar. They come from oceanic islands like Fernando de Noronha, Pernambuco, Trindade, Espirito Santo, Atol das Rocas, Rio Grande do Norte, and even some Brazilian coastal regions. Guanabara Bay is part of the migration route and a potential safe harbor for juvenile turtles during their growth and reproduction. – Source (PT)
1 – My post on the history of the Carioca River
2 – Up until the mid-1800s, slaves known as tigres – due to the stripes made from waste spilling onto their backs – would carry buckets of sewage to dump into the sea.
3 – An aside: The etymology of Arpoador means “harpoon-thrower”, from arpoar (to harpoon), as the rocky outcropping was originally a place where whales were killed.
4 – The Guiana dolphin, or boto-cinza, is a symbol of Rio, depicted on its flag for the last 120 years. Baby Acerola was found in pieces, showing signs of being caught in a fishing net. Researchers suspect it was done by someone not native to the region, since local fishermen know the species is endangered and thus killing one is a crime.