[4][5] The extent of the damage caused by the tailings dam collapse is the largest ever recorded with pollutants spread along 668 kilometres (415 mi) of watercourses.

[16] The Fundão tailings dam was constructed and owned by Samarco, a mining company, near Mariana, a municipality 67 kilometres (42 mi) southeast of Belo Horizonte, in the state of Minas Gerais, Brazil.

The tailings dam was built by Samarco to accommodate the waste resulting from the extraction of iron ore taken from extensive Germano mine, located in the Mariana district of Santa Rita Durão.

The Fundão dam was constructed in hills near the village and subdistrict of Bento Rodrigues, located 14 kilometres (8.7 mi) north of Mariana city.

Bento Rodrigues, which lies 2.5 kilometres (1.6 mi) away in the valley below the dam, was almost entirely flooded by the cascade of toxic water and mud.

[1][3] According to a United Nations report, the tailings slurry traveled 620 kilometres (390 mi) downriver, eventually reaching the Atlantic Ocean.

According to analyses carried out in the city, the mud contains greater than acceptable concentrations of heavy metals, substances harmful to health, such as arsenic, lead and mercury.

[19] There are concerns about contamination of the nearby Rio Gualaxo do Norte [pt], a tributary of the Doce River, due to the toxic substances stored at the facility.

[27] Samarco claimed to have implemented all the recommendations from Ávila, and that the dam was in the process of being heightened when the impoundment reached its maximum holding capacity and began to leak.

However, Samarco failed to comment specifically about the buttress, and claims that it was never warned about the severity of the structural damages, nor about the imminence of a catastrophic failure.

In August 2016, the report of an investigation panel constituted by Samarco and its shareholders was published online [28] The investigation panel findings indicated that the liquefaction flowsliding resulted from multiple factors, including an increase in the saturation of the tailings due to modifications in the design of the dam and the presence of soft slimes in unintended areas on the left abutment of the dam.

Succumbing to external pressure, BHP Billiton, together with Vale and Samarco, signed in 2016 an agreement with the Brazilian federal and state authorities.

Australia's ABC reported that Samarco and its joint venture partners would "establish a foundation to develop and execute environmental and socio-economic programs to restore the environment, local communities and social conditions of the affected areas.

[42] In November 2018, UK-based legal firm SPG Law, now Pogust Goodhead, filed a US$5 billion group action in the High Court of Justice at Liverpool under Brazilian law against BHP Billiton on behalf of 235,000 Brazilian individuals and organizations, including municipal governments, utility companies, indigenous tribes and the Catholic Church.

[51] In March 2023, it was reported that BHP faces an enlarged class-action lawsuit seeking damages of up to U$65 billion for its role in the dam collapse, with the number of claimants more than tripling to 700,000.

[58] On October 25, 2024, mining companies BHP and Vale signed an agreement with the Brazilian government to pay nearly U$30 billion in compensation over the Mariana Dam collapse.

[59] There is speculation that the agreement could end more than one hundred lawsuits against the mining companies in Brazil, and possibly limit legal action abroad.

Vale's vice-president for corporate and external affairs, Alexandre D'Ambrosio, indicated that the compensation deal undermines the foundation of the London case.

[63] The Roman Catholic Archdiocese of Mariana said: "We express our most heartfelt sympathy to the families who have had their homes and property destroyed and those who mourn the death of their loved ones, victims of this disaster of incalculable proportions.

The Diocese of Itabira and Three Lakes and the East Regional II CNBB, comprising the territories of the States of Minas Gerais and Espírito Santo, also issued notes of solidarity with those affected by tragedy.

[65] In fact, the scale of the environmental damage is the equivalent of 20,000 Olympic swimming pools of toxic mud waste contaminating the soil, rivers and water system of an area covering over 850 km.

[66] The company said the tailings that entered the Rio Doce were composed of clay and silt from the processing of earth containing iron ore, which is naturally abundant in the region.

American band Pearl Jam, who performed in Belo Horizonte on 20 November 2015, promised to donate the proceeds of the concert to victims of the disaster.