This study was aimed at recognizing the levels of arsenic, antimony and selenium concentrations in different zones of the lake ecosystem. Total content as well as inorganic species of the studied metalloids were considered. Shallow Lake Jarosławieckie (Wielkopolski National Park) was chosen for the study reported. Water samples were collected in different macrophyte communities of the phytolittoral and in the middle of the lake in early spring and mid-summer 2002. Total concentrations of all studied metalloids in samples collected in summer were lower than in those collected in spring but not all studied mineral species of As, Sb and Se followed the same pattern of changes. Despite seasonal changeability the lack of significant spatial differentiation in the concentrations of the elements studied at the peak of the vegetation season, in particular no differences in their concentrations between the sites in the bulk water in the middle of the lake and the sites in the plant communities was stated. This finding might testify to the fact that the effect of vegetation on the concentration of the elements studied is limited.