Comparative analysis of results obtained in hydrobiological research conducted to date indicates that relatively few water reservoirs in Serbia have been subjected to complex hydrobiological investigations. Apart from the fact that hydrobiological investigations are now performed on only a small number of water reservoirs in Serbia, they are moreover inadequately coordinated, which is especially evident in differences of procedural approaches employed. With adoption of the principles of modern limnology and wider use of new criteria for water classification (m WQI for instance), the current state of hydrobiological research constitutes a basic for the development of comprehensive program of planned continuous studies of water reservoirs in Serbia resulting in their rational and successful management.

This paper presents the most important results on water quality investigation of the Danube river in the Iron Gate reservoir. The investigations are conducted by the Institute Jaroslav Cerni by means of regular monitoring renewed after a long pause in 2001. The determined phenomena are considered in regard to water quality of the Danube river in the upstream zone.

In order to increased the amount of water in Sjenica water reservoir (because of higher production of electric energy by hydroelectrical power plant), stagnant waters of Pester field were irrigated to Vapa river and Sjenica lake. Former swamp areas and theirs life communities, represented specific biological filter in Pester high, a kind of natural lagoons, where big amounts of polluted water with nutrients were spent a processed (especially salts of P and N) were characteristic for exact area because of intensive cattle production. After the irrigation on Pester field, raw, polluted water with the large amount of nutrients by Vapa river get to the Sjenica water reservoir where they represented main cause of eutrophication and degradation of water quality in this aquatorium. Heterogenic and numerous algal association in canal of the Pester field is nearly leftover of previous specific algological flora which testifies the presence of species Chaetophora incrassata Hazen (new habitat in Serbia), the first class water indicator.

The basic purpose of Gruza accumulation is to supply the town of Kragujevac and its vinicity with drinking water. The accumulation occupies large area, comparing with its relatively shallow water and low water mass, which is essential for water eutrophication. The aim of this research is to determine water quality, through index of phosphatase activity at five locations in one year period. According to the results obtained for index of phosphatase activity, water of Gruza lake belongs to 3rd A category. The maximum obtained value (19.60 micromol/s/cubic dm) was determined in the shallow part, at mouth of the river Gruza in July, 2000, and the minimum one (0.39 micromol/s/cubic dm) in the deepest part of accumulation, at location Brana in March, 2001.

In the scope of complex physical-chemical and biological water examination of Bocac water reservoir, the river Vrbas and trbutaries Ugar and Crna Rijeka, examination of standard microbiological indexes of water quality (aerobic organotrophs at 22-26 deg C and 37 deg C, total colliforms and colliforms of fecal origin) was performed during 2002 (March-November). Number of examined microbiological parameters was mainly in the scope of the 2nd water category (beta-mesosaprobic water) with worse water quality in upstream part of the reservoir. Ugar tributary had the best water quality, while Crna Rijeka had the worst status with obvious anthropogenic influence.

Heavy metals contamination of the muscular tussue of nase (Chondrostoma nasus), bream (Alburnus brama) and bleak (Alburnus alburnus) fish species from the Medjuvrsje water reservoir (the Zapadna Mora river), was examined. With the expection of the nase muscular tissue where cadmium (Cd) and mercury (Hg) concentrations above and slightly below MPC, respectively, were detected, the rest of the samples were safe. With the aim of conducting more thorough monitoring of these pollutants, a greater number of elements and a larger number of organisms should be included in the analyses.

The paper presents results of research on hydrophilic flora of the Grosnica reservoir in the Kragujevac basin (Serbia, Serbia&Montenegro). The obtained results confirm that the development of hydrophilic vegetation is dependent on the time, manner, and place of reservoir formation, as well as on the extent of human influence. Analysis of floristic composition of hydrophilic plants of this reservoir indicates presence of 30 species belonging to 20 families. Floristic composition of the hydrophilic flora with flora elements, life forms and ecological factors are presents.

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.

The lack of drinking water in Zajecar was the main reason for building of water barrier on the Grliste river and making the water reservoir. A factory for water processing was also built, but the problems were not disappeared. The conclusion is that the main solution for this ecosystem was in establishing of an monitoring system. That is the reason why we talk out the results of the monitoring and the troubles in this water source as well as in the phases of water processing.

In scope of complex physical-chemical and biological examination of water quality of the Bocac lake, the river Vrbas and tributaries Ugar and Crna Rijeka, examinations of phytoplankton and zooplankton were performed during 2002 (March-November). In qualitative structure of phytoplankton 7 division were registered, with 93 taxa from 49 genera in total. In warmer period extreme domination have fire algae (Pyrrophyta). In zooplankton structure (Rotatoria, Cladocera, Copepoda) 78 taxa were registered from 36 genera, with distinct domination of Rotatoria group. According to saprobiological analysis species of olligo- and beta-mesosaprobic character are prevailing.