The investigations of qualitative and quantitative composition of plankton and the bottom fauna of the Tisza river, Serbia (Yugoslavia), were conducted during 1998. According to the analyses of the indicator species of hydrobionts, saprobic index was calculated, and the estimation of the water quality of the lower flow of the dam near Novi Becej on the structure and abundance of the investigated organisms.

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.

During three years period from 1991 to 1994, investigation of the river Kolubara (Serbia, Yugoslavia) was carried out along 35 km of water course from Valjevo to Lajkovac. The macrozoobenthos community was composed of 117 determined taxa. Of the found taxa Oligochaeta were the most diverse with 40 taxa determined. The greatest diversity of macrozoobenthos community was foound at the river section in Valjevo, upstream the mouth of Gradac (69), while the community was most uniform downstream Valjevo at Bela Stena (24 taxa). A decrease as well as an increase in the macrozoobenthos diversity was not in accordance with similar decrease or increase in saprobic index values since they were in narrow range from 2.37 to 2.59.

According to microbiological parameters, waters of both small rivers of eastern Backa, Serbia (Yugoslavia), are slightly and moderately polluted by organic matter at the most of the investigated localities in summer season. The satisfactory power of water selfpurification has been preserved in these aquatic ecosystems. In order to prevent further eutrophication processes, certain measures of river water protection and conservation should be undertaken, especially in stagnant parts of investigated waters. Also, the regular monitoring of water quality should be established.

During 2001, water from river Cerava and from the littoral where the river flow into lake Ohrid, were examined. Bacteriological analysis included ecological and sanitary aspekt of water state. Heterotrophic, proteolytic, amylolytic and phosphomineralizing bacteria, most probable number of total coliforms (MPN) and presence of Escherichia coli and Clostridium perfringens were determined. The results of investigations shows organic and faecal pollution and permanent negative anthropogenic effects.

In the scope of complex physical-chemical and biological water examination of Bocac water reservoir, the river Vrbas and trbutaries Ugar and Crna Rijeka, examination of standard microbiological indexes of water quality (aerobic organotrophs at 22-26 deg C and 37 deg C, total colliforms and colliforms of fecal origin) was performed during 2002 (March-November). Number of examined microbiological parameters was mainly in the scope of the 2nd water category (beta-mesosaprobic water) with worse water quality in upstream part of the reservoir. Ugar tributary had the best water quality, while Crna Rijeka had the worst status with obvious anthropogenic influence.

The activities acid, neutral and alkaline phosphatases, as well as total phosphatases activities were estimated in the water of the Lake Ohrid tributaries Sateska, Koselska, Velgoska and Cherava. The same analyses were performed in the littoral zones where the tribitaries enter Lake Ohrid. The study covers the period from September 2000 to October 2001. The obtained results show that different types of phosphatase effect different extracellular activities, an observation which is probably the result of differences in the location within the cells and the way of intracellular synthesis.

There have been given research results of quantitative and qualitative indices of communal and industrial waste waters of Nis. The research was carried out by the Institute "Jaroslav Cerni" (group of authors) and JKP "Naissus" (4) with the goal of defining as reliable parameters as possible in order to draw up plans for a central wastewater cleansing plant in Nis, as well as several necessary treatments of the industrial waste waters. There have been presented quantities, load and expected load of the total waste water, basic characteristics of urban and natural recipient, waste water influence on the river Nisava and needed degree of cleansing.

In scope of complex physical-chemical and biological examination of water quality of the Bocac lake, the river Vrbas and tributaries Ugar and Crna Rijeka, examinations of phytoplankton and zooplankton were performed during 2002 (March-November). In qualitative structure of phytoplankton 7 division were registered, with 93 taxa from 49 genera in total. In warmer period extreme domination have fire algae (Pyrrophyta). In zooplankton structure (Rotatoria, Cladocera, Copepoda) 78 taxa were registered from 36 genera, with distinct domination of Rotatoria group. According to saprobiological analysis species of olligo- and beta-mesosaprobic character are prevailing.

Bacteriological examination have been carried out within the comprehensive hydrochemical and hydrobiological investigation of river Koselska during 2002. The aim of investigations is to confirm condition of bacteriological communities and water quality of river Koselska. The results of investigations shows pollution by organic matter. In order to prevent further eutrophication processes, certain measures of river water protection and conservation should be undertaken. Also, the regular monitoring of water quality should be established.