It started as a torrent of mud that flattened a village and frightened neighbourhoods. Now the mineral sludge that killed at least 12 people and polluted more than 600 kilometres of river system has arrived at the Atlantic Ocean, extending its trail of destruction to a delicate marine environment.
The mudflow stems from the failure of the Fundao dam at the BHP Billiton-Vale joint venture Samarco Mineracoes in Minas Gerais, Brazil. The dam burst on November 5, taking with it millions of cubic metres of tailings from Samarco's iron ore operation. At least 12 people are still missing.
The mud buried a number of towns in the south-eastern state, including the worst affected, Bento Rodrigues, 40 kilometres downstream, on its way to the state of Espirito Santo, north of Rio de Janeiro on Brazil's coast.
Since Sunday, the beaches of Espirito Santo at the town of Linhares have turned a bright ochre colour more at home in the Australian outback or the town of Broken Hill, the birthplace of the eponymous Broken Hill Proprietary Ltd (now BHP-Billiton).
On Monday, Linhares council issued a warning for residents not to touch the brown waters, while local fishermen reportedly hired by Samarco started burying the dead fish strewn along the beaches.
A Brazilian biologist, Marcos Vago, told G1, an affiliate of Brazil's Globo media group, that mineral toxins were likely to accumulate in fish stocks, causing supply and health problems. Marine species that visited the river's mouth during their breeding cycles would be the most affected, he said.
The local fishermen's association told G1 that its members were without income after fish stocks the length of the Doce River were destroyed by the sludge.
Brazilian federal judge Rodrigo Reiff Botelho said Samarco must show at a public hearing on Tuesday that it has taken steps to mitigate ecological damage, or risk additional daily fines of R$10 million ($3.7 million).
The miner has already been fined R$250million by the country's environmental agency IBAMA for polluting river waters, causing health risks and making urban areas uninhabitable.
Its owners have also agreed to a R$1billion preliminary deposit fund for repairs and compensation.
Brazilian Environment Minister Izabella Teixeira said on Friday the accident was "the biggest environmental catastrophe" in the country's history. She said it would take 30 years to restore the river.
The clean-up bill could exceed $US1 billion, according to estimates by Deutsche Bank.
Samarco on Monday said the cleaning of the main street of Barra Longa was nearly complete and 100 children had returned to school in the town. Clean-up teams had also cleared road access to surrounding rural areas.
BHP Billiton chairman Jac Nasser last week vowed the company would get to the bottom of the dam disaster.
"We will find out what went wrong. Together with Vale we have agreed to commission an external investigation into the collapse of the tailings dam," he said.
"You have my commitment that we will publicly release the findings. We will also share the results with other resource companies."
For many locals and environmentalists, the results are already obvious. Thousands are living in temporary accommodation, while their livelihoods, the local tourism industry and the economy of two states are likely to take decades to recover.