Abstract In 2015, the collapse of the Fundão tailings dam released millions of cubic meters of mine waste into the Rio Doce Basin, causing profound and lasting environmental impacts. We analyzed 3 years of seasonal variation of water quality and metal concentrations across two middle Rio Doce sub-basins: one impacted by the tailings (Doce River) and a non-impacted reference system (Santo Antônio River). We hypothesized that tailings-associated variables (e.g., turbidity, Mn, As, Fe, Al) would di