With just over a year to go before the city hosts the Games' rowing and canoe competitions, officials with the legislative assembly of Rio de Janeiro Monday launched an investigation into the causes of death both in the lagoon and in other lakes and bays in the state in which this phenomenon has occurred.
The group will work in partnership with the State Environmental Institute (INEA) and the Secretariat of State for the Environment.
Officials defended the belief that the latest rains caused a temperature change of the water and the excess of decaying organic matter, which would have led to a black of oxygen, killing the fish.
The note released by officials highlighted that the amount of dead fish has generated a bad smell and inconvenience to those who live near the lagoon and all the tourists who flock to the area.
Last week, newly obtained video from newspaper O Globo showed a sailor crashing into trash floating on Guanabara Bay.
The incident took place on February 14 and involved professional sailors Breno Osthoff, 20, and Rafael de Almeida Sampaio, 35.
According to Osthoff, the impact was so great the boat was forced onto its side.
Rio de Janeiro has pledged to reduce pollution in the notoriously fetid bay, but last month in an interview with the country's largest sports channel SporTV, Mayor Eduardo Paes admitted that the bay will remain mostly polluted for the games.
"The Olympics are also in a time that has very little rain, then this amount of debris that comes from five municipalities in the metropolitan region, with poor sanitation, is also controllable...I do not see as a problem for the Olympics," said Paes.
Last year biologists said rivers leading into the bay contained a superbacteria that is resistant to antibiotics and can cause urinary, gastrointestinal and pulmonary infections.