The degradation of freshwater habitats by their channelization seriously handicaps ecosystem functioning by impacting their biotic structure, biological diversity and destroying functional links within the ecosystem. Those impacts, superimposed by the disturbances listed in the previous section, reduce ecosystem resilience, impacting selfregulatory processes. Reduced self-purification, together with high pollutant loads, lowers the assimilative capacity of streams and deteriorates water quality. As a result, toxic cyanobacterial blooms were observed in some reservoirs (Izydorczyk, unpublished data), and the concentrations of the produced toxins reached extremely high values of up to 60 ug/l in 2006 (Jurczak, unpublished data).