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Safeguarding migratory fish via strategic planning of future small hydropower in Brazil


Small hydropower plants (SHPs) are proliferating globally, but their cumulative threat to blocking migratory fish and the fisheries that these fish sustain has been underappreciated when compared with large hydropower plants (LHPs). Here, we quantified the trade-offs between hydroelectric generation capacity and the impacts on river connectivity for thousands of current and projected future dams across Brazil. SHPs are the main source of river fragmentation, resulting in average connectivity losses of fourfold greater than LHPs. Fragmentation by SHPs is projected to increase by 21% in the future, and two-thirds of the 191 migratory species assessed occupy basins that will experience greater connectivity losses due to SHPs than LHPs. A Pareto frontier analysis identified future dam portfolios that could halve the number of hydropower plants that are required to deliver the same energy-generation capacity compared with the least-favourable solutions, while simultaneously resulting in lower river fragmentation and protecting numerous undammed basins. Our results highlight the need for strategic planning that considers the unprecedented growth and cumulative effects of SHPs.

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Fig. 1: Temporal trends in river connectivity in Brazil according to changes in DCI over the past century and future projections due to ongoing and planned dam construction.
Fig. 2: Predicted future change in river connectivity.
Fig. 3: Present and projected future river connectivity.
Fig. 4: The effects of SHPs and LHPs on river connectivity.
Fig. 5: Relationship between the generation capacity of each future hydropower project and its effect on river connectivity (DCI) at the basin level.
Fig. 6: Future projections of nationwide river connectivity.

Data availability

All of the analyses were based on governmental (ANEEL, IBGE, ICMBio) or open source datasets, such as HydroSHEDS and HydroBASINS. All references are included in the text. A repository with a research compendium including non-reproduceable data sources, intermediate products, scripts and guidance to reproduce the results is available at Figshare ( The output data generated by our analysis are provided in Supplementary Tables 16.

Code availability

The code used to analyse the data and generate figures are available at GitHub ( and


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We thank J. Zuanon and R. Reis for validating our migratory species list and ICMBio for sharing their dataset on fish species occurrence; D. Li, D. Martins and J. Rocha for the assistance with the analysis. J.D.O. was supported by a H. Mason Keeler Endowed Professorship from the School of Aquatic and Fishery Sciences, University of Washington, who also supported T.B.A.C.; T.B.A.C. received the CNPq/Science Without Borders Fellowship (203991/2014-1), and research grants from Rufford Foundation and National Geographic Society.

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Authors and Affiliations



T.B.A.C. and J.D.O. designed the study, and all of the authors led the writing. T.B.A.C. and M.L.M. worked on the data acquisition, processing and analysis in R, and M.L.M. coded the spatial analysis in Python.

Corresponding author

Correspondence to Thiago B. A. Couto.

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The authors declare no competing interests.

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Peer review information Nature Sustainability thanks Mauricio Arias and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–10, Methods and references.

Reporting Summary

Supplementary Table 1

Estimates of river connectivity loss (DCIp) in the occurrence range of the 365 fish species considered migratory.

Supplementary Table 2

Projected effect of each future hydropower project on river connectivity (DCIp).

Supplementary Table 3

Projected nationwide connectivity loss (DCIp) and generation capacity gains for the favourable future hydropower dam portfolios.

Supplementary Table 4

Estimates of river connectivity loss (DCIi) in the occurrence range of the 365 fish species considered migratory. The DCIi is an estimate of river connectivity loss for migratory fish populations that are predominantly composed of external immigrants from downstream basins (see Supplementary Methods).

Supplementary Table 5

Projected effect of each future hydropower project on river connectivity (DCIi).

Supplementary Table 6

Projected nationwide connectivity loss (DCIi) and generation capacity gains for the favourable future hydropower dam portfolios.

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Couto, T.B.A., Messager, M.L. & Olden, J.D. Safeguarding migratory fish via strategic planning of future small hydropower in Brazil. Nat Sustain 4, 409–416 (2021).

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