Based on the volume of tailings releases and the distance they travelled, the Fundão Dam failure in southeast Brazil (Mariana, Minas Gerais state) was the largest ever environmental disaster in Brazil’s mining industry, and one of the world’s most serious. As they dispersed downriver, the tailings accumulated along the riverbanks and reached the Rio Doce estuary in the Eastern Brazilian Marine Ecoregion. When the dam failed, the mining company and government agencies conducted rapid assessments. But while the government set up a five-year monitoring programme, it took almost a year after the disaster to issue official guidelines and another two years of negotiations and approvals before the data collection began. In this Thematic Report, the Rio Doce Panel looks at government mandated monitoring reports as well as peerreviewed papers, most of which were authored by independent researchers, to assess our knowledge about the disaster’s impacts on marine and coastal areas.