Study sites
We selected three reservoirs in the Czech Republic of different trophic status (from eutrophic Římov to oligotrophic Klíčava), size and hydrodynamics (Table 1). All reservoirs possess canyon-shape morphology with one main inflow (Figure 1), resulting in longitudinal gradients of nutrients and water quality from the inflow to the dam. In summer, the water column is thermally stratified followed by water mixing in late autumn. All studied reservoirs serve as drinking water storages and are therefore restricted to public access. Fish communities are dominated by cyprinids (mainly bleak [Alburnus alburnus ], freshwater bream [Abramis brama ], roach [Rutilus rutilus ]) in Římov and Žlutice, and by European perch (Perca fluviatilis ) in Klíčava despite regular stocking of piscivorous species, i.e. asp (Leuciscus aspius ), Northern pike (Esox lucius ), pikeperch (Sander lucioperca ), wels catfish (Silurus glanis ) (Vašek et al., 2013).