The degree to which any one hydropower plant affects a fish population and its vital habitats varies widely and depends on various aspects including site-specific technical as well as environmental conditions. Thus, risk-assessments need to consider these aspects to provide a sufficient decision supporting tool for commissioning and operating hydropower facilities in terms of fish population conservation. As a first step, species most at risk and their bottlenecks need to be identified.

This report aims to add hydropower related risk values on fish populations to the species-specific sensitivity classification implemented in Deliverable 1.1 (van Treeck et al. 2017). The combined results will provide the baseline for developing a fish population hazard index for the European fish fauna.

Impacts of hydropower on fish populations

The analysis focused on the three principle impacts of hydropower on fish populations:

i) acting as migration barrier to prevent species moving between essential habitats and environments,
ii) hydropower induced mortality during turbine passage,
iii) habitat loss due to habitat degradation and changes in hydromorphological processes especially threatening gravel spawning species

Method and risk classification

Established platforms (Web of Knowledge and Google Scholar) were used to obtain data on turbine mortality and on habitat quality, required for the critical-life stages of fish, using peer-reviewed articles and grey literature in form of reports.

Species were classified at very high risk from hydropower operations if at least three of the four following conditions were fulfilled:

i) belonging to the high or highest sensitivity class adapted from D 1.1,
ii) having high or highest mortality risk during turbine passage,
iii) being diadromous,
iv) being gravel spawners (lithophilic).

Species were classified as high risk in hydropower affected environments if two of the conditions mentioned above were fulfilled, and they were classified as lower risk if only one or none of the conditions were fulfilled.


The sensitivity matrix contains 148 native European fish and lamprey species occurring in European waters. After combining the intrinsic sensitivity of species and the operation related impacts of hydropower 21 and 25 species face a very high and high risk, respectively (Table 1).

Among the species at very high risk there are several candidate species to be considered for environmental impact assessment, as well as mitigation for various river types e.g., the diadromous (migrating between freshwater and marine habitats) salmonids or the large bodied cyprinids like barbel, nase and ide (Table 1 & 2).

Data on habitat quality required for the critical-life stages of fish have been compiled for 38 species including space requirements (e.g. juvenile densities, Figure 1), biological characters and environmental tolerances to guide mitigation measures addressing habitat provision and rehabilitation to enhance recruitment. However, data availability and coherence was limited and thus, allowed only basic estimates.

To sum up, it has to be mentioned that this risk classification is a first attempt which needs further evidencing and practical testing. It is a rather conservative approach, well aware of the tremendous variability and high uncertainties in the underlying data. However, so far the risk classification reflects the state of knowledge as no better and more comprehensive system is available.

For more information download the full report (1MB) or view all technical deliverables.

Nicole Smialek (TUM)

References: van Treeck R, Van Wichelen J, Coeck J, Vandamme L, Wolter C. 2017. D1.1 Metadata overview on fish response to disturbance. Project Report FIThydro D1.1 (