The dynamics and structure of phytoplankton was studied in three nursery fishponds periodically fed with treated household sewage and wastewater from a fruit and vegetable processing plant. The ponds differed with respect to the availability of biogenic compounds (mostly nitrogen). It was found that total phytoplankton biomass ranged from 3.9 to 80.2 mg dm^-3. In two ponds nitrogen content averaged 1.97 and 2.40 mg dm^-3, respectively. Phytoplankton were dominated by diatoms of the genera Fragilaria and Cyclotella in spring, and by green algae of the genera Coelastrum, Coenococcus, Pediastrum, Scenedesmus, and cryptophytes in summer. In the pond with a significantly lower nitrogen content of water (1.37 mg dm^-3) the predominant phytoplankton group were small cryptophytes as mainly Chroomonas acuta and Cryptomonas rostrata, and diatoms of the genus Acanthoceras that were absent in the remaining two more fertile ponds. Green algae Eudorina and Dictyosphaerium were present in this pond only in spring and fall.