Lake-catchment relationships were presented with reference to each part of the subsystem. Ionic loads reflected the potential of the catchment areas and displayed the following pattern: Lake Rotcze < Lake Sumin < Lake Syczyńskie; with respect to every ion, except nitrogen. The highest specific load of ions in Lake Syczyńskie and the strong hydrochemical influence of the lake inlets facilitated the growth of water blooms of cyanobacteria, with a dominance of toxic filamentous P agardhii. It resulted in a poor ecological status of the lake (Q index = 0.8) and its hypertrophy (TSIchl-a = 78). The specific load of ions in the Lake Rotcze catchment (0.23 kg/yr-km(2) of P-PO4) contributed to the good ecological status (Q = 3.2) and mesotrophic character (TSIchl.a = 50) of the lake. Lake Sumin has a moderate catchment influence (2.41 kg/yr-km(2) of P-PO4), which facilitated moderate ecological (Q = 2.1) and trophic (eutrophy; TSIchlSa = 63) status.