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.

As it consequence of soil erosion the contamination of water occurs. Namely, in the soil erosion process on the slopes of watersheds, together with soil particles (sediment) the organic matter, mineral fertilizers and nutrients are washed as well as pesticides applied in the agriculture production. By sediment reaching the water courses and reservoires the mechanical and chemical contamination of water is caused. In the paper sediment transport and losses of humus (organic matter) and nutrients (in the process of sediment transport) are presented in the three small torrential watershed in Western Serbia (Yugoslavia). Average annual specific transport of sediment was in the range between 50.0 cubic meter/year per square km (Lonjinski Potok) and 220 cubic meter/year per square km (Dubosnickog Potoka). In each tone of suspended sediment on average was 73.15-103.20 kg of humus, 2.88-5.93 kg of nitrogen, 0.63-1.50 kg of phosphorus, 2.63-3.81 kg of potassium, 6.76-14.27 kg of calcium and 5.18-9.33 kg of magnesium.

In this paper given are basic characteristics and projected functions of the DTD (Danube-Tisza-Danube) Hydrosystem (Yugoslavia), then types, origin and some characteristics of muds - sediments in the hydrosystem channels. It is estimated that in hydrosystem channels gets in averagely about 1.28x10**6 tons of deposits annually, and of that amount in channels are settled about 0.64 x 10**6 cubic meter annually. In 1980-1996 period, it is mudded from channels of the main channel network averagely about 0.19 x 10**6 cubic meter/year, and in 1991-1996 period, usually only about 0.056 x 10**6 cubic meter/year, i.e. about 10 of average amounts which are deposited during the year. Also explained are numerous undesirable influences of muds - sediments on water quality in channels, as well as functions of the DTD (Danube-Tisza-Danube) Hydrosystem in general. At the end, measures for gradually improving conditions that are influenced by muds - sediments are, proposed.

Testing performed by five glass cups has been a try to show form and extent of water reservoir soil base influence on its water quality. At the some time a possibility of alleviation of eutrophication by means of certain safety precautions have been examined. During the test performed on a model of parameters (water temperature, air temperature, O2, chlorophyll a, total nitrogen, etc) have been monitored. The results of actions reffer to a fact a soil base influences deterioration of water quality, especially immediately after water reservoir filling, but the mentioned negative influence of the soil base could be decreased applying certain safety precautions.

5 water samples were taken from the irrigation channel nearby Kamendin, Sirig, Becej, Backo Gradiste, Backi Petrovac which is part of DTD (Danube-Tisza-Danube) system (Serbia, Yugoslavia). Content of Cd (cadmium), Pb (lead), Hg (mercury), As (arsenic), Cr (chromium), Ni (nickel), F (fluorine), Cu (copper), B (boron) in water samples was analyzed. The origin of these elements in the waters and the effect of potentional pollutant was analyzed. Also, deviation of content of these elements from permissible amounts which were announced in the Book of Regulation was commented.

This paper analyzes the results on water quality in the Medjuvrsje water reservoir (Serbia, Yugoslavia) in the period 1994-1997. The water reservoir was erected for the needs of electric engineering in 1953 as far as 182 km along the Zapadna Morava river stream issuing from the Ovcarsko-Kablarska crag. All the tributaries of the Zapadna Morava flow in torrents, thereby depositing drift onto reservoir and inducing eutrophication process. Water regime in the water reservoir is conditioned by power plant operation, with daily oscillations about 30 cm causing turbulence in aquatic biota, including fish as the most developed aquatic vertebrate by their evolution level and greatest in biomass. Hydrochemical and some hydrobiological parameters influencing productivity of the water reservoir, were assessed. From hydrochemical aspect, this water reservoir contained water, the quality of which was found to be within 2nd-3rd class. The water was, however, loaded with high concentration of NH3, Fe, BPK5 and suspended substances inducing its quality to be out of the class range.

During the period 1990-1997, the content of 11 trace metals (Fe, Cr, Co, Al, Mn, Cd, Cu, Ni, Pb, Zn, Sr) was studied in muscle and other organs of fish from DTD (Danube-Tisza-Danube) channel system (Yugoslavia). According to obtained and analysed data, the trace metal bioaccumulation can possibly act as enviromental indicator in biomonitoring. DTD (Danube-Tisza-Danube) Channel System can, therefore, be classified as the 3rd class, concerning analysed trace metal content.

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.

The protected natural goods of the swamp Zasavica is situated in the north part of Macva (Serbia, Yugoslavia). It is parallel to the flow of the Sava river, which leads to the fact that it used to be the riverbed of the Sava and also of the Drina river. It is interesting for its variety of the plant and animal species. The investigations have been done during autumn period 1997, when the investigated groups were the most heterogeneous. It included algae, Rotatoria,Cladocera, Copepoda and Hydracarina. Among algae, Bacillariophyta were dominant. Among all the investigated groups Rotatoria were the most heterogenous, with great number of the species that are rarely present. Also, some Cladocera species were rare. The estimation of the water quality is given according to the bioindicator species.

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.