Guanabara Bay, the historic gateway to Rio de Janeiro, is both a UNESCO World Heritage Site and one of the most polluted coastal ecosystems in the world. It sees 18,000 liters (4,755 gallons) of sewage released into its waters every second. Domestic garbage, industrial waste, appliances, furniture and even corpses can be found floating in the bay’s murky waters.

And yet, the Guanabara resists, thanks to the dedicated and fearless efforts of civil society, including popular movements, academics, policy advocates, and environmentalists like biologist Mario Moscatelli.

For decades, Moscatelli has been fighting to preserve what’s left of Rio’s native mangroves. “When you fly over the mangroves of Guanabara Bay, you see them full of garbage,” says Moscatelli. “What takes me 20 years [to build], some guy destroys in a week. And there is no reaction from the government, despite the law being clear on protecting these ecosystems.”

A recent study estimates that the annual economic cost to Rio de Janeiro state caused by the pollution of the bay is at least 31 billion reais (around $6.5 billion) due to the loss of fishing in addition to the added strain to an underfunded health system and the loss of tax revenue from real estate devaluation. The environmental recovery of Guanabara Bay is important not only from an ecological point of view but also for public health and for the economy of Rio de Janeiro.

In June 2021, after decades of broken promises to clean up the Guanabara, Rio’s government privatized sewage treatment and sanitation services. The concessionaires promise to treat 90% of all wastewater by 2033 and invest a total of 30 billion reais (more than $6 billion) over 30 years to improve sanitation. Águas do Rio, one of the concessionaires, reported after its first year of operation that its investments prevented “the daily release of 1 million liters [264,000 gallons] of raw sewage into rivers, canals and the Guanabara Bay.” Based on the most recent estimates from 2014, this amounts to just 0.06% of the total.

But Moscatelli remains cautiously optimistic. He has partnered with the private concessionaires to recuperate degraded mangroves and he also works with local schools, government and the public to encourage the protection, monitoring and the revitalization of Rio’s mangrove ecosystem. “It’s a drop in the sea of what needs to be done,” admits Moscatelli. “It is a calling, despite the dangers, despite the challenges. I choose to insist,” he says of his commitment.

Mongabay collaborated with reporter Andrew Johnson, who has been following Moscatelli’s work for years, to produce this short documentary.

Banner image: Biologist Mario Moscatelli (right) supervises the work of a colleague during the replanting of mangroves in Jardim Gramacho, close to a disused dump. The area is the most polluted part of the bay and exists under the shadow of the city’s infamous criminal organizations. Image by Andrew Johnson.