Various physical, chemical and biological methods are used in complex investigations which are aimed at determining the quality of water. One of the oldest but also most widely accepted biological mathods is determination of saprobity on the basis of bioindicators. In application of these methods the existing lists of the indicators are most frequently used (Sladacek 1973, SEV 1977). In these lists only nine types of red algae (Rhodophyta) are specified as indicators of water quality. One of the main trends in development of algaeology in Serbia (Yugoslavia) is investigation of autoecological properties of algae and making a list of water quality indicator algae suited to the specific ecological conditions in water ecosystems of Serbia (Yugoslavia). The objective of this paper is to present information about apperance of red algae in the rivers of Serbia (Yugoslavia) and influence of physico-chemical factors upon their development, which represents a contribution to making of the above mentioned list of the water quality indicator algae.

Processes of transformation of organic matter are slowed down so that cellulose which originates from cell walls of Sphagnum is retained long in unchanged form. The highest valises of cellulolytic bacteria (0.33-126.67 bact/ml) were recorded in October. In most cases slightly active species were found, Cellvibrio fulvus was dominant. The participation of fungi in cellulolytic community was significant 23-31.5.

Within the comprehensive hydrobiological investigation of Grosnica water reservoir (Serbia, Yugoslavia) composition and dynamics of bacterioplankton, phytoplankton and zooplankton, as well as their seasonal successions were studied. The composition of plankton communities varies during the vegetation period in the function of the physicochemical features. Grosnica water reservoir with its microbial features belongs to the 1st-2nd class of bonity according to Kohl. The highest values pf bacterio- and zooplankton were recorded in August, while bruto primary production in September.

The paper presents one of the methods for calculation of temperature of a water course, downstream of the relase of a thermo-electric power-plant, taking into consideration the well-known temperatures and discharge values of the tributaries under different meteorological conditions. In view of the importance of temperature regime for the water eco-system, understanding the influence of the power plants on thermic capacity of the water course, is essential in design and use of the power plant. The author's intention is to help towards improving computer models for the computation of a water course thermic capacity. To this end a model developed at the Institute for Meteorology and Water Management in Poland and applied in many coutries has been presented.

During the 1996-1997 period, dynamics and structure of zooplankton and benthos in sugar mill canal in Crvenka (Serbia, Yugoslavia) were studied. Two representative sampling sites were chosen, while the third one served as a control site, providing it has no impact on cage culture. The canal section where the cages were established, had previously been drainage and dredged. Immediately after the refilling, the zooplankton qualitative structure was scarce, with dominating Rotatoria. Two months later, the situation improved and Cladocera and Copepoda emerged. Those two groups of organisms have the major role in enhancing the commercial feed consumption Soon after the refilling, the benthos was reestablished. Sample analysis shows the presence of Oligochaeta and Chironomidae. Qualitative and quantitative analysis of benthos points out no significant difference between the canal sections upstream and downstream the cage culture.

Mathematical modles and adequate investigation works enables successful water quality modeling. These models includes all relevant abiotic components (concentration of dissolved oxygen, temperature regimes and temperature stratification, concentration of organic and inorganic components of physical-chemical water conditions), while the biotic components are present only with phyto- and zooplankton. In new water reservoir, ichthyofauna mostly undergo mancontrolled successions, starting with planned stocking a water reservoir with fish. The paper presents analytical approach for mathematical modeling of ichthyofauna and application of Lotka - Volterr's equations.

In this paper the short review of the results of calculation of the coincidence between the water level and quality parameters at the gauging station Cuprija-rail bridge (Serbia, Yugoslavia) is presented. The basic principles of the applied method and criteria for the estimation of the statistic significance of coincidence indicators are given. At the end of the analyses and comments of the obtained results, as well as the possibility for application of this methodology are given. The paper gives numerical quantities of the estimated indicators of statistical significance of the coincidence of water level and quality parameters of groundwater. Also, the graphical illustration, which shows the common exceeding probabilities of the water level and quality parameters, is presented.

Using the then years data series of organic load (COD, BOD), ammonia and organic nitrogen, total phosphorus, detergents and oxygen dissolved, a heavy pollution of Bega Canal at the Romanian - Yugoslav Border ("Srpski Itebej" Control Station) is illustrated. High load of organic matters and nutrients as well as extremely low oxygen dissolved content created anaerobic conditions in aquatic environment, are the main characteristics of Bega Canal state at the analyzed location. As the Bega Canal (left tributary of Tisza river) is an international river, a transboundary issue of pollution is considered in this paper.

In this paper the results of determination of natural waters from the territory of the township Smederevska Palanka and Rekovac (Serbia, Yugoslavia) are presented. The content of metals in waters was determined by the AAS method and other parameters were determined by spectrophotometric and potentiometric method.

In previous works numerous specific changes of water composition in the Danube backwater effects Iron Gate 1 reservoir (Yugoslavia), have been initiated. By studies of conditions of generation and composition of sediments, the models denying importance of assumption on sedimentological features of deposited materials foreseen by the project, have been established, as it was confirmed with more details by newer investigations. The new data on the character of sediments coincide in all elements with changes of water composition, which was formerly presented, thus the knowledges of these phenomena being in that way more important. The data on composition of the deposited material, the macro and micro-composition are of great importance to perceive the influence of new sediments to the quality of surface and groundwater, especially of the sources for water supply, then in a long term for the sudden high risk processes corresponding to a chemical time bomb. Data have confirmed validity of the model of intensified deposition of allochthonous material with plankton and influence of this phenomenon to the processes trough the downstream section.