The paper presents results of the hydroecological investigations of the Vlasina river basin, Serbia (Yugoslavia). The researches were performed in May and September 1996, as a part an annual investigation cycle. Samples were collected from five localities on the Vlasina river, and on two spots on its main tributaries - the Gradska river and Luznica, just before entering into the Vlasina. Qualitative and quantitative data on composition of phyto- and zooplankton, periphytic and benthic communities together with data obtained from physico-chemical water examinations were analysed to assess water quality of examined water courses. The results of performed monitoring were compared with informations on the sources of pollution, as well as with the data on hydrology, geomorphology, demographic variations, and recent development of tourism and industry in the Region in order to assess environmental quality of aquatic ecosystem and to suggest the conservation strategy.

From two locations in the Vizelj channel (Serbia, Yugoslavia) in the early spring and before irrigation water samples were systematically taken in order to examination the content of harmful and dangerous matter. Content of Cd, Pb, Hg, As, Cr, Ni, F, Cu, B in water samples was analyzed. The origin of these elements in the water and the effect of potentinal pollutants were analyzed. Also, deviation of content of these elements from permissible amounts which were announced in the Book of Regulation was commented.

Important differences in the structure of fauna communities of their deepest parts of benthos were found in the investigation of several water reservoirs (Gruza, Grosnica, Barije, Bor, Vlasina and Medjuvrsje) on the territory of Serbia (Yugoslavia) lasting several years. The pronounced alterations of the structure are in the correlation to the pronounced degree of eutrofication was also established according to other indicators, above all according to the concentration of biogenic salts and the amount of organic substances. Characteristic group and taxa of the fauna of benthos which point to certain level of eutrophications were separated.

In this paper sediment production and sediment discharge and its influence on hydroenergetical potential as well as pollution of river Lim - upper flow, Montenegro (Yugoslavia), were taken into consideration. Besides of problems of sediment and water discharge protection - biological and technical measures for sanation the negative effects of erosion processes were recommended. Total annual sediment production for the river Lim - upper flow was 679,763 mE-3/year and annual sediment discharge was 312,013 mE-3/year. Such sediment (produced and discharged) has negative impact on the hydroenergetical potential and soil resources and also pollutes water with sediments and other harmful and hazardeous materials. Introduction of erosion control measures will reduce the negative effect of erosion on the tolarant level.

Oxygen aspect of water pollution of Skadar lake, Montenegro (Yugoslavia) is considered in this paper. Water analysis data in the period of 1991-1998 were used to establish relevant parameters, oxygen saturation (%O2), and five day biochemical demind (BPK5). Those data were supplied by Hydrometeorological Institute in Podgorica, Montenegro (Yugoslavia). Measurements were taken from three places in northern part of Skadar lake, where the increased water pollution is expected, and from southeastern part of the lake, out of source of pollution directly influence. According to results from this research, there is close relation between water pollution and oxygen water balance. Parts of the Skadar lake with low water circulation are especialy susceptible (place Kamenik). In the 1991-1995 period, this phenomena is manifested with variation depending of the chosen area and year. After some improvement of water quality in the 1996-1997 period, there is noticeable increase of water pollution in 1998 at all places. Supersaturation was identified by the percentage of O2 in Skadar lake area at whole.

Reproduction and planktonic phase of life of edible shellfishes, Mytilus galloprovincialis Lamk. and Ostrea edulis L. were the subject of the investigations. Biological and ecological characteristics of mentioned species have been studied in Boka Kotorska Bay (Adriatic Sea), Montenegro (Yugoslavia), having in mind data from the Adriatic Sea and Mediterranean. Beside, some localities from Boka Kotorska Bay, conveniet for their rearing, were described , too. A period of their appearance in plankton was considered before all.

The main characteristics of catchment area of Boka Kotorska Bay (Adriatic sea, Montenegro, Yugoslavia), are high slope, carstic structure of ground, high precipitation (over 5000 mm a year) and high run-off of rain water. All rainwater is transported trough carstic ground structures quickly appearing in numerous sources along the sea cost or ones located on the bottom of the Bay. The large volume of freshwater which permanently empty into the Bay has the strong influence on the aquatic environment (salinity, temperature, transparency, etc.) and biota (abundance of the species) as it has been observed in the parts of Boka Kotorska Bay (i.e. Morinj and Risan Bays). The abundance and number of species are the good indicator of changes of aquatic environment and hydrological changes as well as of the capability of aquatic organisms to adapt quickly on the severe changes of conditions.

The results of long standing and systematic monitoring of quality of river Danube's water, done by the net of stations for controllingquality of water of the Republic Hydrometeorological Service of Serbia (Yugoslavia) are given in this paper. The amount of organic matter (HPK, BPK5), concentration of dissolved oxygen, nutritive matters (NH4(+), NO2(-), NO3(-) and total PO4(3-) and conductivity are specially examined. The results are shown depending on seasonal measuring (average values for spring, summer, autumn and winter) during the period 1995-1998, and the changes are analyzed.

Alcohol and yeast production is the most important part of the biotechnological production in Yugoslavia, with annual production of 13 667 867 liters of absolute alcohol and of 20 947 490 kg of yeast in the year 1998. Large environmental load is produced by wastewaters from alcohol and yeast factories (512 000 P.E.), especially by alcohol stillage (BOD 40 000 - 50 000 mg/L). Anaerobic treatment is suitable process for treatment of alcohol stillage, and of yeast factory wastewater. In this paper, effects of treatment process (organic load reduction, energy of produced biogas) are discussed; and potential of anaerobic treatment os wastewaters from Yugoslavia's alcohol and yeast factories is reviewed.

In April 1997 and 1998 investigations of algae, Rotatoria, Cladocera, Copepoda and Hydracarina were conducted. The investigated localities were 8 small water bodies at around 800 m a.s.l., at Mali Krs, in the surrounding of Bor, Serbia (Yugoslavia). The aim was to examine composition of these groups and to give the evaluation of the quality of water. Among algae, according to the number of taxons, the dominant group was Bacillariophyta (45), then Chlorophyta (17), Cyanophyta (3), Euglenophyta (4), Xanthophyta (1) and Pyrrophyta (1). Rotatoria were present with the highest number of taxons among microfauna. In these investigations 48 taxons were present. The highest number of taxons was among Cephalodella, Corurella, and Trichocerca. Among Cladocera 4 taxons were present, and among Copepoda 9 taxons, and all the present species were found in our previous investigations. Hydracarina were present with 3 species, also with high diversity. Around two thirds of all taxons are oligosaprobionts, which indicates to the good quality of the water.