The paper deals with the results of the phytoplankton investigations carried out in the 7 localities along the Yugoslav section of the Tisza river in the period of 13 Februar - 3 March 2000, after accidental pollution with the cyanide and heavy metals. Although certain decrease in the density of the phytoplankton and variation in the qualitative and quantitative composition were recorded, there are no significant differences in comparison with the data before accident. The short-term and possible long-term consequences were recognized, having in mind ability of algae to accumulate pollutants into their cells, and that algae are the first link on food chains. Since the content of pollutants increases with every next member in the chain, it is easy to assume cumulative effect of the all previous members.

During complex studies of phytoplankton, the role of particular phytoplankton groups was examined, as one of important indicators of eutrophic processes in the Bay of Boka Kotorska (Adriatic sea, Montenegro (Yugoslavia)). Throughout summer 1999, investigations have been performed at representative locations (Kotor, Tivat and Hercegnovi bays) at the depths of 0, 5, 10 and 20 m. Maximal values of microphytoplankton were found in Kotor Bay in July (2.1 x 10**6 cells/cubic dm). In Tivat Bay, maximal values of microphytoplankton were found in June, although they were ten times lower (2.4 x 10**5 cells/cubic dm). In the Bay of Hercegnovi, mean values were lower, while maximal quantity of microphytoplankton was found in August (2.6 x 10**3 cells/cubic dm). In the Boka Kotorska Bay, the maximal percentage of 95% of the group Bacillariophyceae was found in the most productive surface layers at the depths of 0 and 5 m. The impact of eutrophication was the most visible in the Kotor Bay. It decreased towards the open sea. Diatoms populations (Bacillariophyceae) were dominant in the Bay, while the participations of other groups is insignificant. Consequently, it means that Bacillariophyceae are the most adapted group to the eutrophic conditions of the Boka Kotorska Bay.

The analysis of the phytoplakton and phytoperiphyton communities in the Palic lake (Serbia, Yugoslavia), has been performed with aim the water quality evalution. The determining and following proportional presence of phytoplankton were in the fourth sector of lake during 1998, 1999, and 2000. During the period of investigation, the phytoplankton community was characterized by forms of Chlorophyta, Cyanophyta, Euglenophyta and Bacillariophyta. During the investigation it was perceived the change in proportional participation in the presence of the four alga group mentioned above. The most representative percent was the Chlorophyta group, with values from 44.4%, to 54.7%. The other phytoplakton group has less values of percentage in the values.