The research concerned the influence of copper ions on the content of pigments in the leaves of Lemna minor , which shall be used for biotesting of the polluted water of the surface impoundments. The studies were carried out in the model experiments. The plant Lemna minor was kept in the solution of copper sulfate having different concentrations. The amount of pigments was determined using the spectrophotometric method. The content of chlorophylls and total number of carotenoids was determined by the Lichtentaler formula. The copper ion has a toxic effect on the Lemna minor plants, which influences the growth and the content of pigments; the photosynthesis processes are suppressed.