Continuing earlier studies in the area of the Sulejów Reservoir, further research was carried out in the season 2002 into the effects of various environmental factors on the bloom yields of cyanobacteria and the synthesis of cyanobacterial hepatotoxins – microcystins. The second part of the paper looks at chemical factors such as the concentrations of biogenic substances and chosen metals (Ca, Mg, Zn, Cu, Ni, Co, Mn, Cr, Cd and Pb) in water. The levels of microcystin-LR in the cells of cyanobacteria were negatively correlated only with the concentration of nitrates(V), total nitrogen and dissolved organic nitrogen. The ratio of total nitrogen to total phosphorus did not show any effect on cyanobacterial bloom yields or the efficiency of microcystin production. No effect was also found for the metals, probably because of their quite low concentrations in water in the season 2002.

45-62