Paraopeba River in Brazil remains unsettled six years after dam collapse

Nearly six years after the B1 tailings dam collapsed at Brumadinho, Brazil, the river that received the waste has still not settled into a stable state. That is the conclusion of four years of monitoring, with the full study published in Water Biology and Security by researchers at the Federal University of Minas Gerais and partner institutions.

The research team sampled 19 sites along the Paraopeba River and its tributaries every two months from October 2020 to August 2024, 23 campaigns, and identified more than 532,000 bottom-dwelling invertebrates from 304 groups of insect larvae, worms and snails. These animals live in the river bed, react quickly to changes in water and sediment quality, and are used worldwide to measure river health.

“We expected the affected reaches to slowly converge on a stable community after this much time,” says lead author Diego Castro. “What we found instead is a river that keeps being reshuffled. Species disappear and others arrive, campaign after campaign, and that has not slowed down.”

Rather than counting species, the team measured how much each community changed over time and separated that change into species lost and species gained. “Communities turned over strongly at every site whether they were affected or not,” Castro says. “This points to a basin under chronic pressure from untreated sewage, agriculture, sand dredging and older mining on top of the tailings.”

Notably, in the reaches that received tailings, high flows during the rainy season stir the fine sediment up again and reset the community before it can stabilise.

The tributaries, meanwhile, told a different story. They held 265 of the 304 groups recorded, including 49 found nowhere else in the basin, and they act as reservoirs of regional diversity and sources of recolonisation for the damaged channel.

“Tributaries are not just reference points on a map — they are where the biological diversity of the basin is held, as well as the source of the animals that recolonise the damaged channel,” Castro says. “If we lose them, the main river loses its way back.”

Further, the team found that the main threat is no longer the disaster itself, but the chronic stress returning with every rainy season on a river already burdened by other pressures. “Recovery in mining-impacted rivers is neither linear nor uniform along the channel,” Castro adds “Protecting tributaries and their connections to the main river should be central to restoration.”

Contact the author:

Diego Marcel Parreira de Castro, Departamento de Genética, Ecologia e Evolução, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. diegobioufla@gmail.com

Funder:

This study is a product of the Damage Assessment Programme on Biotic Environment (PDD), developed and coordinated by Amplo Engenharia e Gestão de Projetos and the Universidade Federal de Minas Gerais and funded by Vale S.A. as part of its obligations to repair the damage caused by the collapse of the B1 dam.

Conflict of interest:

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

See the article:

Castro, D.M.P., Solar, R., Paglia, A., Vieira, F., Salles, F.F., Rocha, I.C., Gagliardi, L.M., Moura, M.N., Dornas, T.T., Paprocki, H. (2026). Spatial and temporal dynamics of macroinvertebrate assemblages along a mine tailing impacted river. Water Biology and Security. https://doi.org/10.1016/j.watbs.2026.100687