The Amazon contains over 4,000 miles of rivers inside the world’s largest tropical rainforest. This enormous river basin is supported by numerous upstream tributaries that begin in the Andes mountains, stretching across five culturally and politically diverse nations. Current and proposed dams along major tributaries threaten the connectivity and diversity of the ecosystem. Most assessments of the river network ignore the interconnectedness of the waterways and the unique traits of individual tributaries. However, new research has closely documented for the first time the proliferation and impact of hydropower along the Amazon and its Andean headwaters.
Hydropower dams are much more prevalent than previously estimated: the study found 302 existing or proposed dams, nearly two times higher than previously reported. Peru has the highest number of existing and proposed dams (170), and Columbia the lowest (zero existing dams and one proposed).
Most dams disrupt connectivity in tributaries rather than the mainstems of the Amazon. However, this is likely to change under future dam development scenarios that would lead to greater losses of network connectivity.
The Andean Amazon holds more fish diversity than previously accounted for. In the first estimate for the region, almost 700 species of fish were accounted for at >500m elevation. There are an estimated 3500-5000 species of fish in the Amazon overall, including numerous migratory species that depend on river connectivity.
The presence of dams influences many natural and cultural processes downstream, such as sediment deposition, carbon storage, continuation of protected area status, and cultural connectedness of indigenous peoples.
In the Andean Amazon region, the effect of hydropower dams can only be fully understood when considered cumulatively and synergystically. More international cooperation and better transboundary management are needed to protect river connectivity throughout the entire watershed. All Amazonian countries recognize the value of intact forests, but this view needs to be extended to include intact river systems as well.
Anderson, E. P., C. N. Jenkins, S. Heilpern, J. A. Maldonado-Ocampo, F. M. Carvajal-Vallejos, A. C. Encalada, J. F. Rivadeneira, M. Hidalgo, C. M. Cañas, H. Ortega, N. Salcedo, M. Maldonado, and P. A. Tedesco. 2018. Fragmentation of Andes-to-Amazon connectivity by hydropower dams. Science Advances 4(1): eaao1642. DOI: 10.1126/sciadv.aao1642.