Water samples collected from two lakes separated from each other by the cascade of four small lowland reservoirs were subjected to analyses in order to compare contamination levels in these ecosystems. Inductively coupled plasma mass spectrometry was used to determine eight elements: Al, As, Cd, Cr, Li, Mn, Sb, and Zn. Statistical methods were applied in order to assess the degree of self-purification of water, during its flow from Swarzedzkie Lake to Malta Lake. Obtained distinctly, lower concentrations of all studied elements in Malta Lake than in Swarzedzkie Lake indicated the role of self-purification processes, which occurred in the distance between these lakes.

In order to characterize the contamination of the Swarzedzkie Lake and generate elemental distribution patterns 18 elements have been determined in samples of water, taken just above the bottom sediments. Analyses were carried out using two instrumental techniques - ICP-OES and ICP-MS. Two main sources of contamination were identified - diffuse pollution from agriculture and stormwater from the town. Three separate groups of elements were distinguished using cluster analysis and two groups using principal component analysis. These three groups are characterized as geogenic elements (Ag, As, Mg and Sb), elements supplied by the agricultural catchment (Ca, Mn, Sr, Na, K and Al) and elements originated from the urban contamination (Ni, Cr, Cu, Fe, V, Ba, Zn and Pb). PCA differentiated the above group of urban elements from the rest, originated from diffuse sources, with exception of alluminium, which was situated between two distinguished groups.