The aim of this research was analysis of the species composition and planktonic algae biomass in the post-mining water ponds. These ponds are located in Kozy in the area of the closed quarry (it was closed in 1994) on the slopes of the Small Beskid. In the closed quarry there was once a sandstone mine. The analyses of these reservoirs water were conducted during the vegetation season in 2018 year, in monthly intervals. The chlorophyll a concentrations were measured using a spectrophotometer, while the phytoplankton biomass was calculated by comparing the shape of algae to geometrical figures and calculating the volume. The chosen chemical parameters (i. a. phosphates, pH and conductivity) were also determined. The values of the planktonic algae biomass and the chlorophyll a concentrations were low. In these ponds the typical algae for oligotrophic water were observed (Pinnularia Ehrenberg, Achnanthes lanceolata (Brébisson ex Kützing) Grun. in Cl. & Grun.), but there were also periodically the species characteristic for gently eutrophic water (Nitzschia acicularis (Kützing) W. Smith).