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).