There are estimated to be about 26,000 locations where a hydropower turbine could produce electricity in the UK. Previous studies on larger hydropower schemes have indicated that the potential environmental impacts of such schemes include: changes in fish population structure; habitat alterations; loss of crucial spawning and nursery habitat; loss of biological diversity; modifications to water quality and hydrological regimes; barriers to fish migration, and disruption of longitudinal connectivity. There are concerns that small hydroelectric schemes may cause similar environmental problems and any impacts may potentially lead to changes in fish population dynamics and thus, deterioration of the river ecological status, which contravenes obligations under the EU Water Framework Directive to achieve good ecological status or potential in all surface water and ground water in all Member States (European Commission Directive 2000). These small hydroelectric schemes may cause direct mortalities to fish (e.g. where fish encounter turbines) and/or indirect mortalities (e.g. where delays to migration make fish more vulnerable to predation). However, there appears to be an acute lack of hard evidence about the impacts of run-of-river schemes on fish passage at single structures, the potential cumulative impacts of a series of structures throughout a river basin, and on the freshwater ecosystem. This limited understanding compromises our ability to develop effective mitigation measures based on sound science, or to conduct the cost-benefit analyses necessary to balance the advantages of renewable energy developments against their potential impacts on fish populations and freshwater communities. In this study, the migration behaviour of European eel (Anguilla anguilla) was studied by means of acoustic telemetry in relation to an in-river hydropower station in the River Frome. The results of this study can provide information that will form the basis for advice on the impacts of small in-river hydropower schemes on migratory species.