The investigations of dynamics and composition of plankton, bottom fauna and fish community have been done at three localities (1-inflow, 2-the middle, 3-dam) at the Barje water reservoir (Serbia, Yugoslavia) during 1997. During winter period diatomea Asterionella formosa was dominant at all the localities. At the same time among zooplankton species Rotatoria group was dominant, with the emphasis of Polyalthra dolicoptera at the locality 2, while Keratella cochlearis was dominant at the localities 1 and 3. The present species are oligo- and betamezosaprobionts. Among the investigated bottom fauna species Oligochaeta and Chironomidae were present. The number of oligochaeta was between 1665-7878 ind./square m. By qualitative analyses the domination of Tubificidae family was present. It is known that the presence of this group of organisms and it's high number indicate the organic pollution of ecosystem. 30 individuals of the bighead, (Hypophthalmichthys nobilis) with the average weight of 5.6 kg was captured by net.

The kinetics of phytoplankton is complicated function of phytoplankton present and their differing reactions to solar radiation, temperature and balance between nutrient availabilities and phytoplankton requirements. Computers program for water quality problems helps users interpret and predict water quality responses to natural phenomena. But model parameters and initial condition needs hydrodynamic and hydrologic measures in long time interval, with combination of laboratory studies. Lake Gracanka (Serbia, Yugoslavia) is good example for description of the processes kinetics of phytoplankton. But, simulation model can not be used to guide future monitoring efforts without needing measuring and developing network of measuring station.

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.

Studies of phytoplankton in the Montenegrin coastal sea (Adriatic Sea), Montenegro (Yugoslavia), have been done in August and September 1998. Simultaneously, investigations were carried out in the area of Boka Kotorska Bay (Kotor and Tivat Bays) and outside the Bay, i.e. in the zone exposed to the influence of the open sea (Petrovac and Budva). It was found that the density of microphytoplankton is higher during summer, than in the autumn. So in the summer-period, as a consequence of stronger eutrophication process, mean-value of microphytoplankton density was 10**5 cells/cubic dm, and in autumn 4 x 10**4 cells/cubic dm. On the contrary, mean-value of nanophytoplankton density was higher in the autumn (5.2 x 10**6 cells/cubic dm) than in summer (3.5 x 10**5 cells/cubic dm), being a consequence of a decreasing eutrophication during colder period of the year. Having in mind the direct influence of the open sea outside the Bay, it is intelligible that population density of both phytoplankton size-fractions is lower along the Montenegrin coast, than in the Boka Kotorska Bay (Montenegro, Yugoslavia).

The present paper cites results of studying phytoplankton in the Grosnica Water Reservoir, Serbia (Yugoslavia). Seasonal investigations during 1997 and 1998 enabled us to establish composition and structure of the phytoplankton community, quality of the lake's water, and its trophic status. During the period of investigation, the phytoplankton community was characterized by forms of Cyanophyta, Pyrrophyta, Chrysophyta, Bacillariophyta, Euglenophyta and Chlorophyta. Qualitative analysis indicated that algae of the divisions Bacillariophyta and Chlorophyta are dominant in the phytoplankton, while saprobiological analysis using bioindicatory algal species showed that water of the Grosnica Water Reservoir during the given period was of the 1st and 2nd quality class.

In this paper, some data on long term seasonal investigation of hydrography and plankton are presented. The most important fact is that the whole area is exposed to the impact of the freshwater from numerous sources from the coast and submarine springs in Boka Kotorska Bay, as the impact of rivers Bojana and Drim. Exchange of the intermediate water-masses between Adriatic and Jonian basins is of great importance, too. So, basic ecological data, as well as characteristic phytoplankton and zooplankton groups and species are described.

In the period October 2001 through November 2002 in six series parallely with physico-chemical and hydrobiological analyses, the content of photosynthetic pigments was determined in algae in the region of flow-through reservoirs of "Djerdap 1" and "Djerdap 2" on the profiles of Smederevo, Ram, Veliko Gradista, Donji Milanovac, Tekija, Kladovo and Radujevac. The samples were taken by a pump from the river midstream at the depth of 1-0 m (composite sample), while in the vegetation period April, June and September, the samples were taken at the depth of 5 m. The peak concentration of chlorophyll-a, the biological indicator of trophic condition, was recorded in the month of April in the Smederevo profile (30.2 mg/cubic meter) at the depth of 1-0 m. The lowest values of chlorophyll-a in all studied cycles were recorded in the Radujevac profile (below the dams) with the mean annual value of 1.8 mg/cubic meter. Chlorophyll-c occurs as the subdominant photosynthetic pigment. Values of chlorophyll-c were higher than chlorophyll-a in the month of June on the Donji Milanovac profile in the analysed sample taken at the depth of 5 m. Higher values of chlorophyll-b were recorded in the course of the vegetation period in the month of June on the profiles of Smederevo, Ram, Veliko Gradiste and Donji Milanovac at the depth of 1-0 m.

Investigations of phytoplankton were done in the shallow Montenegrin coastal sea during the period from June to December, 2002. These investigations were the continuation from the preceding years. The main intention was to establish the impact of eutrophication to the quantity and composition of phytoplankton i.e. to establish the difference between areas in the bay and outside the bay. Like is previous years, the highest quantities of phytoplankton - microphytoplankton above all, were found in the area of the Boka Kotorska Bay (in Kotor Bay), Montenegro (Serbia&Montenegro). In July, 2.1 x 10**6 cells/cubic dm were found with dominant species Leptocylindrus minimus represented with 1.4 x 10**6 cells/cubic dm. In the area outside the Bay of Boka Kotorska, exposed to the impact of the open sea, values were significantly lower. In front of Budva, maximum was 1.7 x 10**5 cells/cubic dm in July. At locality exposed to the influence of the river Bojana (brackish water), similar values were established, except in October when 1.1 x 10**6 cells/cubic dm were found.