In this work influence of different concentrations of linear active substance (LAS-DBS) on activity of Serranus scriba CUV have been studied. Desynchronization of circadian rhythms is in direct correlation with LAS growing concentrations. The high disproportion was found between maximum permitted concentrations (3 mg/l) and our results which show the changes in fish behaviour at 0.2 mg/l LAS.

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.

In this paper, we are consider processing of soils erosion and his way on protection expoitation of water for population water supply, melioration's systems for irrigation and for strew of manger of the Lim river with the tug and suspend bank (Montenegro, Yugoslavia). We are given suggestions for protective utilization of agricultural and forest lands and the possibilities of water exploitation from Bistrica river (Montenegro, Yugoslavia). That is useful for fishing, irrigation, energetic, tourism and water supply. In this paper, you can meet some suggestions about exploitations of minerals and organic fertilizars that are not toxics and they not any influence on pollution of land and water.

During the 1994-1995, seasonal investigations of the fountainhead and spring region of the river Susica, near Uzice in West Serbia (Yugoslavia) were carried out. The bottom fauna composition, termic properties of air and water as well as chemical parameters were also determined. By the study of bottom composition 26 taxa were determined. The most uniform fauna was found in the Susica fountainhead while its diversity was increasing farther downstream the spring region.

During the period from 11th May, 1991 to 5th March, 1994, seasonal study of the river Jablanica (Serbia, Yugoslavia) macrozoobenthos was carried out. Investigations were done of three sectors: in the upper, middle and down reach of the river, with the aim to estimate water quality changes by the changes in bottom fauna composition. Bottom fauna community was composed of 17 invertebrate groups with 100 taxa determined. The most diverse Oligochaeta (21 taxa) and Ephemeroptera (19 taxa). Macroinvertebrates diversity decreased downstream the river as a result of the pollutional degree increase. Saprobic indices were from 1.51 (sector 2) to 1.8 (sector 3).

In Yugoslavia, application of macrozoobenthos for the purpose of bioindication has been relatively limited. This communities has been used in conjugation with saprobiological methods, while biotic indexes have been unjustifiable used to a small extent. This paper shows the most significant biotic indexes used in the World and possibility of their application in Yugoslavia, as well as the necessity for their modification and elaboration of new ones specific to Yugoslav conditions.

The river Gvozdac (Serbia, Yugoslavia) is a small hill water current. It is situated on the mountain Goc and it belongs to the river basin of the river Ibar. During 1965, water micro-reservoir "Gvozdac" on the river Gvozdac was built for the hydroenergetic purposes, with the capacity of about 30,000 cubic meter and the maximum depth, in the present situation of about 2.5 m. Algological and saprobiological enquires have been performed on the water micro-reservoir, on the very river Gvozdac, on the river Ribnica and on some smaller stagnant waters on the given area, in the period between 1988-1994. The analysis have been shown that under the influence of antropogenic factors changes became apparent in the confluence and structure of algae flora as well as a degradation of water quality. The example of water micro-reservoir on the river Gvozdac indicates the destructive processes which are being developed in water micro-reservoirs and which should be stopped, as the significance of the small stagnant waters are not only in keeping and improvement of qualities of greater aquatorials and water tributaries of the river basins but also in the storing of biodiversity of aquatic assotiations in river basins (as well as in algae flora as one of the components).

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.