Functional traits describe species in respect to functional characteristics and therefore complement taxonomic information. Although several studies investigate environmental impacts caused by hydropower dams, few have focused on long-term patterns of functional and taxonomic fish diversity; changes in functional structure, in particular, are largely unknown. In this study, we investigated long-term changes (10 years) in taxonomic and functional diversity across environmental gradients created by the construction of Peixe Angical hydropower dam, Tocantins River, Amazon Basin. Our results revealed trends of functional and taxonomic stabilization 10 years after river regulation, in the different zones of the reservoir. Both the functional and taxonomic diversity showed progressive decrease over time, reaching more stable levels after 6 years. As expected, the increase in fish abundance registered soon after damming was followed by a marked decrease in all sites. We observed strong alteration in functional and taxonomic composition over the years, with more stable values after the sixth year. The most abundant species in the river period virtually disappeared after river damming, replaced by species with adaptations to cope with the environmental filters created by the impoundment. In addition, our results showed that the loss of functional diversity occurred stochastically; despite the loss of functional profiles with the loss of species, it was not possible to determine functional convergence. In conclusion, Peixe Angical hydropower dam induced strong changes in the taxonomic and functional structure of fish assemblages, with trends of stabilization ten years after river impoundment, in the different zones of the reservoir.
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