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.

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 1996 (March and June) the mineral water "Rudovci" was sampled in its spring in the village Rudovci, Serbia (Yugoslavia). The physical-chemical analyses have shown that the temperature of the water was 180 deg C with sodium-carbonate content. It has been considered that the quality of water was variable in a short period from 3 months. Comparing the analyses of the mineral water from 1996, we can consider some remarkably distinctions in some chemical elements. The chemical analyses made in 1996, have shown changes in following contents: magnesium (47.6 and 64.5 mg/l); sodium (1313 and 1355 mg/l); iron (2.35 and 3.76 mg/l); boron (5.2 and 4.8 mg/l); arsenic (0.08 and 0.06 mg/l). In 1974, the chlorine content was 28.4 mg/l, but about 218 mg/l in 1996. The nitrate content varied from high (19.2 mg/l) in 1974 to low (about 0.75 mg/l) in 1996.

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.

Mountain Goc is one of the regions with the highest water potential in Central Serbia (Yugoslavia), with specific annual runoff of 12-17 l/s per square km. Upper part of the catchment area of the Gvozdacka River has 111 springs, on the surface of 13.3 square km. 33 springs has volume yield from 0.5 to 2.5 l/s, with physical and chemical parameters of high water quality. These springs never dry up, even during years with low amount of precipitation. The upper part of the catchment area of the Gvozdacka River is under association Abieti-Fagetum, which is one of the worthiest in Serbia (Yugoslavia). Besides annual amount of precipitation, characteristics of soil, hydro-geological attributes of rock masses, influence of vegetation on processes of interception and evapotranspiration, which are very important factors for preservation of springs and their volume yield, also the system of forest ecosystems management. Not adequate measures in exploitation of forests lead to decreasing of volume yield of springs, and often to their disappearing.

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.

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.

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.

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.