Today, it is still stinky, sludgy and clogged with trash. Precarious shacks line its filthy shores.

"The Riachuelo generates a hub of sickness, a hub of insecurity and it cripples commercial development," said Alfredo Alberti, head of the neighborhood association of La Boca, a gritty but touristic area bordered by the channel.

Although cleanup efforts have failed in the past, activists are optimistic because of the Supreme Court's intervention and the fact that Argentina has attacked the environmental safety of two pulp mills being built along a shared river in Uruguay.

Eduardo Mondino, the nation's public advocate, said the government "discovered" Argentina's pollution problems after it challenged the Uruguay pulp mills on contamination grounds.

"External and internal circumstances have put environmental policies in the forefront and made the Riachuelo an unavoidable issue. So I think we'll see progress made," Mondino said.

President Nestor Kirchner has increased the clout of his environment secretariat and put a long-time activist, Romina Picolotti, at its helm last month.

Picolotti said detoxifying the Riachuelo is a top priority, but it would be "scientific insanity" to give a timeline.

"The Riachuelo has not only swallowed boats, it has swallowed programs and government officials. People are tired of empty promises," Picolotti told Reuters in an interview earlier this month.

SUPREME PLAN

The Matanza-Riachuelo river basin is home to more than 10 percent of Argentina's total population. The public advocate's office has said heavy metals such as lead, chrome and mercury pollute the water, soil and air, and may cause chronic health problems.

A lawsuit by neighborhood groups led the Supreme Court in June to order the federal, provincial and municipal governments and 44 companies to clean up the Riachuelo, citing people's constitutional right to a healthy and clean environment.

The government has yet to formally release details of its cleanup plan, but elements of it have been widely leaked in media reports citing government officials.

According to the reports, the plan includes the eventual relocation of some companies from a petrochemical hub and strict controls on remaining plants. More than 3,500 industries operate in the river basin.

The petrochemical hub is home to the "flammable slum," which grew up above a toxic dump. Half of the children there are reported to have lead poisoning, along with respiratory and dermatological problems.

Media reports said some of the families living there will be relocated under the government plan, which includes the declaration of an "environmental emergency" in the area. Picolotti said work to cut pollution in the Riachuelo should begin in October.