Speculation about the cause of the smell has also focused on the wide inequality between the wealthy neighborhoods close to the lagoon and the favela slums on the hillsides, many of which still have open sewers that flood each February and March. Some blame the poor infrastructure in the favelas. Others suspect rich condominiums around the lagoon are bribing officials to secretly discharge their waste.
Moraes dismisses such rumors. The biggest problem, he says, is an unloved species of fish called the savelha, or menhaden, which spawns in the lagoon. After the eggs hatch in January and February, the fish grow until there is no oxygen left in the lagoon. Birds will not eat them because of their spiny skin and fisherman are reluctant to catch them because the flesh tastes awful. Even dog food factories have turned their nose up at these fish, which are left to die because the link to the sea is too narrow for them to leave at this time of the year, Moraes says.
Eduardo Pacheco Jordao, a professor at the Federal University of Rio de Janeiro, is less inclined to blame the savelha, though he agrees the problem is historic and organic, rather than recent and sewage-related.
“History shows this happens whenever there is a sharp fall of the temperature,” he says, explaining this causes muddy, organic material on the bed of the lagoon to rise to the top.
As it degrades, it sucks the oxygen out of the water.
“It’s a very old problem. And people have known what to do about it for many years — improve the renovation of water in the lagoon by widening and deepening the canal from the sea — but they would rather put up with the occasional smell than the construction,” he says.
That may have been true in the past, but with the world about to visit Rio for the World Cup and the Olympics, officials are pressing ahead with an alternative deodorizing scheme.
The city and national government recently approved a plan to build four 2.8m diameter pipes under Ipanema at an estimated cost of 40 million reals. This would allow more oxygen into the waters of the lagoon and make it easier for the savelha to swim out. Another 20 million reals will be spent on expanding the nearby Leblon beach, which has lost been losing sand to the canal. Bidding on the contract is due to start in August.