Dead fish appear near Billings Dam

The Environmental Company of the State of São Paulo (Cetesb) is investigating the appearance, since Sunday, the 8th, of a large number of dead fish in the Estoril Park, in São Bernardo do Campo, near the Billings Reservoir, in the metropolitan region of São Paulo. According to the municipal administration of São Bernardo, aquatic activities in the area have been suspended and the authorities have been called “to investigate the causes of the problem”.

There is still no information about what caused the animals’ deaths. The fish were found in a branch of the Rio Grande, near the region of the water source used to collect water and distribute it to cities in the ABC Paulista region, such as São Bernardo do Campo, Santo André, Diadema and São Caetano.

The State Basic Sanitation Company (Sabesp) states that the water supply “operates normally and without interruptions in the water treatment process”. It also says that the water is collected from the Rio Grande arm, “which is separate from the Billings Reservoir”.

In recent weeks, the state has recorded low humidity due to the lack of rain, high temperatures and a large concentration of pollutants brought from fires spread across different regions of the country.

When water has a high concentration of organic matter, bacteria end up using oxygen for respiratory processes, reducing the concentration of the gas available to fish.

According to a note from Cetesb, the company’s technicians went to the site and collected samples with the aim of checking the characteristics of the water “and understanding the reason for the fish deaths”. The work was carried out by teams from the ABC I and ABC II Environmental Agencies, and technicians in Aquatic Ecotoxicology and the Sampling division.

“The managers of Estoril Park, on the banks of the Billings dam, were also recommended to collect dead fish,” said Cetesb in the statement.

Also in a statement, the city government of São Bernardo do Campo reported that it had suspended activities in the municipal park and said that authorities had been called to investigate the case. “The Administration is awaiting the results of an expert assessment carried out by Cetesb to allow the resumption of water activities at the site,” it said.

The municipal administration also highlighted that Billings “is the responsibility of EMAE (Metropolitan Water and Energy Company), of the State Government”.

Biologist and professor at the University of São Caetano do Sul, Marta Angela Marcondes went to the site on Monday and lamented the presence of dozens of dead fish in the dam arm.

“All you see are dead fish in one of the arms (of the Rio Grande), right at the entrance to the park. When I arrived earlier, the fish were more towards the middle, and now, because there is wind, they are reaching the edge,” she said, in a video posted on social media.

“It’s sad to see all these animals dying and we collected the water to find out why these animals died. The oxygen is well below what we usually see in this arm,” the biologist added.

Sabesp states that the water supply “operates normally and without interruptions in the water treatment process”. It also says that the water is collected from the Rio Grande arm, “which is separate from the Billings Reservoir”.

The company also reports that it “carries out constant monitoring, from the source to distribution” and adds that analyses and quality control are carried out daily to meet the “potability standards required by health and health surveillance agencies”.

Drop in oxygen concentration is a frequent cause of death

“Dissolved Oxygen (DO) is a limiting factor for the maintenance of aquatic life and self-purification processes in natural aquatic systems and sewage treatment plants,” informs Cetesb. “One of the most frequent causes of mortality is the drop in oxygen concentration in water bodies.”

The minimum value of dissolved oxygen (DO) for the preservation of aquatic life, established by the Resolution of the National Environmental Council (Conama) is 5 mg/L, but there is a variation in tolerance from species to species.