Small hydropower plants, large consequences: why low environmental impact in legislation does not mean low impact on migratory fish
Year: 2026
Type: article
Abstract: Migratory fish provide food, income, and key ecosystem services for hundreds of millions of people worldwide. Hydropower development is widely recognized as a major threat to these species, with impacts often assumed to be proportional to project size or operational type. However, this assumption overlooks a key ecological feature of migratory fish: their dependence on spatially connected habitats to complete their life cycle, particularly spawning grounds. By blocking access to these critical reproductive areas, both small and large dams can disrupt migration routes, reduce reproductive success, and ultimately compromise entire populations. Despite this, projects classified as “small” are often treated as low-impact and may undergo simplified environmental assessment, even when they pose substantial ecological risks. In this Policy Forum, we argue that the impact of hydropower projects on migratory fish, regardless of their generation capacity, can only be properly estimated using a multi-scale framework, grounded in ecological connectivity, population dynamics, and cumulative basin-scale effects.
Language: English
Subfield: Nature and Landscape Conservation
Field: Environmental Science
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7221776282