Tons of rotting fish have filled a lagoon in Rio de Janeiro, Brazil where Olympic rowing and canoeing events will be held during next year's Games. Over the past week, thousands of the silver fish have died and have been scooped out of Rodrigo de Freitas lake, but city authorities and biologists have argued about the cause. More than 37 tons of fish have been collected, according to Rio's waste management company, but there is still an overwhelming stench, sparking complaints from neighbours and passers-by. Clearing: Rio's waste management company said it has cleared more than 37 tons of fish, which have been taken to the city's main dump . Olympics: Rodrigo de Freitas lake is set to host the Olympic rowing and canoeing events during next year's Games in Rio de Janeiro, Brazil . There is an overwhelming stench coming from the lake and authorities and biologists have argued about about the cause of the deaths . Rubbish collectors will continue to rake the decomposing fish, a small silvery species called twaite shad, off the water's surface until the the mass dying subsides. They are being taken to the city's main dump. The die-offs are common in Rio, where rivers, lakes and even the ocean are blighted by raw sewage and garbage. Rower and Olympic hopeful Felipe Xavier said: 'I have to come train but these dead fish bother us because the smell is very strong and the huge amount of fish slows the boat.' But Alexandre Fernandez, rowing coach of Botafogo club based in Rio, said he had no worries about the phenomenon and  believes the cause was natural, not because of pollution. In February, twaite shad died  in the blighted waters of Guanabara Bay, where the Olympic sailing events are to be held. Members of a local rowing club have to train among the dead fish in Rodrigo de Freitas lake ahead of the Olympic Games in the city in 2016 . Rubbish collectors will continue to clear the decomposing fish, a small silvery species called twaite shad, off the water's surface in Rio . More than 37 tons of fish have been collected, according to Rio's waste management company, but there is still an overwhelming stench . The dead fish are being scooped out of the water by rubbish collectors using nets and are then taken to Rio de Janeiro's main dump . Rio's environmental secretariat has insisted that the latest incident is the result of a sudden change in water temperature. 'The intense rains that happened last week and a rise in the sea levels led to a spike in the (sea) water entering the lake, causing a thermal shock,' it said in a statement, reporting that water temperature in the lake quickly fell by 4C. However, several scientists have rejected that explanation, saying that pollution is really to blame. Estefan Monteiro da Fonseca, an oceanographer at Fluminense Federal University, said the official explanation 'makes no sense'. Despite more than 37 tons of the fish being removed from the water, there is still an overwhelming stench which has prompted complaints . Picturesque? Rio de Janeiro's stunning landscape has been blighted by the dead fish, which are currently being cleared from the water . Lagoon: There are so many fish on the surface of the lake in Rio de Janeiro, Brazil that almost no water can be seen in some places . Alexandre Fernandez (not pictured), rowing coach of Botafogo club, said he's not worried and believes the cause of the deaths was natural . He said: 'The lake continues receiving large quantities of sewage.' He added that it has large concentrations of sulfur because of the organic material dumped into it, and depending on the wind, that material rises to the surface and kills fish. Rio's water quality has become one of the most contentious issues heading into the 2016 Olympics. Authorities have long said  the games would be the catalyst for a major cleanup of the city's waterways, but as the  sporting event approaches with few improvements, they are now admitting that the Olympic promises won't be met. Natural causes? Rio's environmental secretariat has insisted that the latest incident is the result of a sudden change in water temperature . Passers-by have to hold their noses because of the overwhelming stench coming from the surface of the water, where rowers are training . Rubbish collection: A man sits on a boat filled with dead fish in Rodrigo de Freitas lake, where Olympic events are due to be held next year . Training: A man rows in the lake surrounded by thousands of dead fish ahead of the Olympics in the South American city next year . Rio Governor Luiz Fernando Pezao acknowledged earlier this week 'there's not going to be time' to finish the cleanup ahead of the games, suggesting it might take until the end of 2018 instead. Sailors have repeatedly voiced concerns about possible health and safety threats posed by competing in Rio's waters. Mr Fonseca warned that if another fish die-off occurs during the games in August 2016, 'Rio's image could suffer irreparable damage'. Rio Governor Luiz Fernando Pezao acknowledged earlier this week 'there's not going to be time' to finish the cleanup ahead of the games . An oceanographer said that if another fish die-off occurs during the games in August 2016, 'Rio's image could suffer irreparable damage'. Authorities have  said the games would be the catalyst for a major cleanup of the city's waterways, but there have been few improvements .
Tons of dead fish are being cleared from a stinking lagoon in Rio de Janeiro, Brazil, which will host Olympic events . Rotting silver fish have filled Rodrigo de Freitas lake where rowing and canoeing events should take place next year . There is an overwhelming stench and authorities and biologists have argued about about the cause of the deaths .