Officials say thousands of hectares of land and water affected by “country’s worst environmental catastrophe ever”.

A mudflow thick with toxic mining waste, which initially spilled earlier this month from the collapse of two tailings dams into a main river in southeast Brazil, has now reached the Atlantic Ocean, says Brazil’s environmental agency, Ibama.

Ibama told Al Jazeera on Sunday that thousands of hectares of land and water in the region have been affected by what has been described as the country’s “worst environmental catastrophe in history”, after the flood of sludge travelled at least 500km through the Rio Doce (Sweet River) over the past few weeks.

On November 5, about 60 million cubic metres of iron ore waste – an amount that could fill around 25,000 Olympic-size swimming pools – engulfed and devastated Bento Rodrigues and Paracatu, two districts in the state of Minas Gerais, and contaminated the river, which was a primary source of clean water and food in the region.

At least 11 people were confirmed killed, 15 went missing, and hundreds of homes were destroyed.

Authorities are struggling to find 15 people still missing more than two weeks after the disaster [Ricardo Moraes/Reuters]

The extent of environmental damage is still being measured, according to Brazil’s Ibama agency.

Some people living in fishing and farming communities along the river say their livelihoods have been severely hurt by the disaster.

As biologists struggle to contain the environmental damage, Brazil’s Environment Minister Izabella Teixeira said it could take up to 30 years to clean up the Doce basin.

Meanwhile, the government is probing the cause of the collapse of the dams in a step towards taking civil action against the mining company, Samarco, an Australian-Brazilian joint venture that owns the dams, after punishing it with a $100m fine.

Samarco has agreed to pay more than $250m in compensation over the disaster.

In a statement to Al Jazeera, Samarco, one of the world’s largest producers of iron ore, said that inspections by authorities last July indicated that the dams “were totally safe”.

“Samarco also performs its own inspections, according to the Federal Law of Dam Safety, and has an operations team working a 24-hour shift for the maintenance [of the dams] and identification of any abnormality,” it said.

Hundreds of people have been displaced [Ricardo Moraes/Reuters]

The company also detailed its efforts to provide relief and compensate victims.

“Samarco is distributing water to the places affected by the mud. On November 9, 158 families – representing 612 people – were provided accommodation in hotels in Mariana’s region by Samarco.”

“There were seven available helicopters for rescue operations and the company delivered 600 emergency kits [composed of mattresses, linen, towels, blankets and materials for personal hygiene]; 3,800 snacks and meals were available, and 10,000 bottles of water were delivered.”

Samarco added that it was in the process of providing 700 temporary houses for the victims.

It also said it was working to build wells in the region in an effort to remedy the clean water shortage.

The disaster has ignited calls for stricter regulations for the storage of mining waste in the country.