BUENOS AIRES--At its broad mouth on the edge of Buenos Aires, the Riachuelo River looks more like a lake than a river. The water seems to be barely moving. It is dirty and smelly. And it may be more like a sludge pit than a lake, a sludge pit festooned with floating islands of plastic bottles and soda cans, rainbow blotches of oil and diesel fuel, clumps of newspapers and plastic bags, tree branches, water-logged planks and truly foul garbage that no one should have to look at.
If prizes were awarded for pollution, the Riachuelo, also known as the Matanza-Riachuelo, would be in contention for a gold medal. People here like to say it is the most polluted river in the world. They are probably wrong. But it may be the most polluted river in Argentina - and that, in itself, is a very competitive zone.
Now an ambitious clean-up is underway. The Supreme Court of Argentina has ordered that the river, which winds through 40 miles of the capital city of Buenos Aires and Buenos Aires Province, be scrubbed and that the thousands of factories along its banks be compelled to stop desecrating it with the residue of leather tanning, the bloody remains of slaughtered cattle, the full range of petroleum fuels and a paralyzing list of industrial chemicals. The court also demanded that communities stop dumping raw sewage into the river.
The World Bank is lending Argentina $840 million. Among the things the money will pay for are sewage treatment plants and hook-ups to the homes of many of the perhaps 4 million people along the river who have always lived without their own toilets. Congress has created the National Authority of the Matanza-Riachuelo Basin to replace a tangle of government agencies that had been responsible for overseeing the river but had done virtually nothing. A federal judge, Dr. Luis Armella, has been appointed to enforce the Supreme Court order.
All of this sounds like a new day for a river that has been a health hazard and an eyesore for generations. But people in Buenos Aires are skeptical. "I'll believe it when I see it," said Diego Dillenberger, the editor of the bi-monthly magazine Imagen in Buenos Aires.
Mr. Dillenberger and the people of Buenos Aires have witnessed several false starts on the Riachuelo. In 1993, Maria Julia Alsogaray, Argentina's Minister of the Environment, vowed to revitalize the Riachuelo in a thousand days. Two years or about 730 days later, President Carlos Menem promised pleasant days of boating, fishing and swimming. Ms. Alsogaray was later accused of corruption, including siphoning off money designated for work on the river. In 2006, another Argentine Minister of the Environment, Romina Picolotti, arrived with another earnest pledge. In that same year, the Supreme Court issued the clean-up order that now seems to be gathering steam.
Argentina has some of the most severe pollution in the world. The country's leaders have mainly ignored the issue and there has been little public clamor. I walked alongside the Riachuelo recently, the brightly painted and charmingly tilted old wooden houses of the La Boca neighborhood of Buenos Aires over my shoulder. A musky, briny odor rose from the water. It has been that way for decades - unchanged by the occasional flash of interest.
But this time, says Dr. Armella, the judge appointed to fix the sick river, it is going to be different. He sounds like he means it. I spoke with him at a conference in Buenos Aires sponsored by Greenpeace. "This is a process that has started," he told the audience of perhaps 100 environmentalists, "and it will not stop. Perhaps we will not get it done very quickly. But we will work steadily. And we will never stop."
Environmental experts say the work could easily take 20 years. Within a few years health conditions could be markedly improved.
Economic tension is bound to rise. Under the court order, factories must retro-fit or close. Some workers will lose their jobs. Dr. Armella says he is going to be "respectful of private interests" but he also says there is going to have to be a cultural change.
He is bracing for reaction and hoping to avoid years of litigation. "The companies should not be spending money for lawyers," he told the conference. "They should be spending money on the clean-up."
Juan Carlos Villalonga, a senior executive of Greenpeace in Argentina, and other environmentalists say they are encouraged, but also wary. "We always felt that we were working with the wind against us," Mr. Villalonga said. "Now we feel the field has been leveled."