"Now, the net only brings garbage, garbage, garbage. And we can't survive that way," the 60-year-old told AFP, as a team of volunteers including a two-time Olympic sailing champion endured record heat this week to collect hundreds of sacks of plastic waste in a clean-up drive on the island.

The tiny island is a magnet for waste in Guanabara Bay -- the site of one of the world's most postcard-perfect views and a graveyard of failed plans to clean up waters flooded with rubbish, raw sewage and chemicals.

Fishermen like Crispin receive a payment for helping in the clean-up initiative to make up for his loss of income.

The drive to clean up 80 tonnes of waste suffocating the shores of Pombeba is led by former sailor Juliana Poncioni, 37, director of the Nas Mares ocean conservation organization.

Guanabara Bay provided one of the biggest headaches during Rio's hosting of the 2016 Olympics, as sailors complained about floating trash and filthy waters despite a rush of clean-up measures.

Two-time Olympic sailing champion Martine Grael and other members of her SailGP racing team were also among around 50 volunteers involved in the clean-up.

"What we really want are actions that make a difference," said Grael, 34.

Poncioni said emerging patches of sand from under the trash "bring hope," but the untenable situation should also be a wake-up call for politicians.

"This problem is not in Guanabara Bay or Brazil or Rio de Janeiro, it is a global problem," said Poncioni.

"We have to stop the plastic tsunami. As humanity, we produce 400 million tons of plastic per year, and 11 million end up in the ocean."

A team of researchers from the Biotema environmental monitoring group was also on the island, studying the presence of microplastics -- which have been found on the highest mountain peak, in the deepest ocean trench and scattered throughout almost every part of the human body.

"Once consumed by aquatic microorganisms, (microplastics) are transported to our body, causing toxicity," said team leader Andre Salomao, while placing samples of sand and plastic waste in glass containers.

The dire state of the waters in Guanabara Bay again came under the spotlight last month when Rio de Janeiro and the neighboring city of Niteroi presented their candidacy to host the 2031 Pan American Games.

Water and sanitation operator Aguas do Rio in 2021 signed a contract to spend millions of dollars to clean up the bay.

When presenting their candidacy for the Pan American games, authorities renewed their commitment to properly treat the wastewater of 10 million residents living around the bay in Rio and other municipalities, by 2030.