At the 1992 Earth Summit a grand plan was drawn up to tackle pollution in Rio's Guanabara Bay, but 20 years on the once-pristine fishing ground is a cesspool of garbage and toxic waste.

Guanabara at one time had healthy mangroves, sandy beaches and a rich ecosystem, but decades of urbanization and deforestation have taken their toll on waters now choked full of household garbage and sewage.

Fishermen blame the dwindling fish stocks on a massive oil leak in 2000, which saw nearly one million litres of crude spew into the bay from an underwater Petrobras pipeline.

"In the past, a day of fishing would bring 300 kilograms (660 pounds) of fish and between $40 and $50," 62-year-old fisherman Milton Mascarenhas Filho told AFP.

"Today, we get 30 kilograms and between $5 and $10 dollars," said Filho, president of the fishermen's association in Mage, a town on the northern shore of the massive bay, which runs past Rio de Janeiro to the sea.

A $1 billion program to depollute the bay was launched at the 1992 Earth Summit with funding from the Inter-American Development Bank (IADB), Japan's International Cooperation Agency and the Rio state government.

But 20 years later, there is little to show for it.

"It was the biggest clean-up program ever undertaken in Rio state but many mistakes were made and a great deal of the works have not been completed," local government official Gerson Serva told AFP.

-- Landfill and oil leak --

Ahead of the June 20-22 Rio+20 summit, which seeks to build on the Earth Summit 20 years on, Brazilian authorities have closed one of the more blatant symbols of the bay's degradation -- the Jardim Gramacho landfill.

Set up on ecologically sensitive wetlands 34 years ago, the seaside mountain of malodorous trash that saw some 8,000 tons of waste processed every day was one of the biggest landfills in the world.

Environmentalists had been crusading for its closure for years, blaming poor waste management at the site for much of the toxic leakage into the bay.

But it is the 2000 oil leak from a refinery belonging to state-owned energy giant Petrobras that experts believe is most responsible for the contamination that ruined the bay.

Petrobras, which was fined $28 million for the disastrous leak of some 338,000 gallons of crude, has spent more than $200 million over the past decade on environmental and social projects in the area.

Cruising through the bay reveals a startling amount of floating detritus. Clothes, shoes, sofas and television sets can be found bobbing along in the mangrove swamps hugging its shores.

"Guanabara Bay is today a huge cesspool and garbage dump," biologist Mario Moscatelli who has been leading the fight to clean up pollution in Rio state since 1997, told AFP.

Serva explained that some 15 municipalities in the area are criss-crossed by rivers that dump 20,000 liters of wastewater per second into the bay.

Of this total, only a third is treated and only 10 percent of the rest goes trough a natural process of decomposition.

-- Progress can be made --

State authorities recently signed a new, $640 million contract with the IADB to build and develop sewage networks in towns around the bay.

Moscatelli said it would take two decades to clean up Guanabara, even if short-term actions are already showing some results.

The "Living Mangrove" project, set up in Mage 12 years ago, shows that it is possible for the ecosystem to recover.

Run by the non-governmental group Onda Azul, it has used reforestation to turn an area of 1.6 square kilometers (0.62 square miles) into an ecological park.

A system was created to protect young mangrove seedlings with plastic bottles that are only removed when the trees are strong enough to cope for themselves.

Nearly 120,000 square meters (1.3 million square feet) of ground has been replanted and a second area of 160,000 square meters has seen 40 percent of its vegetation restored.

"The mangrove is a real marine cradle," Adeimantus da Silva, one of the project's authors, told AFP.

"We have recorded many birds, mammals and reptiles. Several fish species and 70 percent of crabs are already reproducing in the restored mangrove."