Canonical Correspondence Analysis (CCA) ordination diagrams of drinking water-supply reservoirs showing the site distribution along the first two axes based on the relationships between species and environmental variables: (A) vectors – environmental variables, grey empty circles – samples from spring season, grey full circles – samples from summer season, black full circles – samples from autumn season; numbers of reservoirs are those used in Table 1; abbreviations of hydromorphological and geographical parameters are those used in Table 4; full line – group 3, dotted line – group 4, dashed line – group 5, (B) codes of diatom taxa according to OMNIDIA version 5.5.