In this paper there were given research results obtained during many years of investigation of hydrophytes of the Tisza river, Serbia (Yugoslavia), and their bioindicating values. The plant world of the Tisza river is characterized by floristical diversity, with three characteristics band: band of submerged, band of floating and band of emerged hydrophytes. Among submerged plants these are distinguished by abundance, covering values and occurrence degree: Ceratophyllum demersum, Elodea canadaensis, Potamogeton crispus, Potamogeton perfoliatus and Potamogeton pectinatus. In the floating band species of the fam. Lemnaceae: Lemna minor, Lemna gibba, Spirodela polyrrhiza and Potamogeton fluitans are most frequent. In the closest coastal band, these species are most frequent: Typha angustifolia, Typha latifolia, Phragmites communis, Sagittaria sagittifolia and Typhoides arundinacea. On the basis of determined floristical composition and bioindicating values there can be noticed the organic pollution increasing trend.

Removal of natural organic matter (NOM) from groundwater by aluminium sulphate and polyaluminium chloride (PACl) was investigated. The maximal decrease of UV absorbance at 254 nm was near 70%. Decrease of permanganate value about 50% was achieved by PACl coagulation. Similar effect can be achieved using 2.5 fold higher concentration of aluminium sulphate. Coagulation process at pH 5.5 was successful with 3-5 times less concentration of coagulant. The heterogenous composition of NOM in water had been changing by coagulation. The total trihalomethane formation potential is 50-60% lower in coagulated water. The greatest removal was success for chloroform precursors.

There was investigated potential erodibility of two small experimental watersheds, which belongs to the watershed of Topciderska river, Serbia (Yugoslavia), on the base of geological structure of the watershed area. The investigations of potential erodibility of watersheds were included the analysis of tectonical and every geological formation, as from viewpoint of its possible erodibility as well as of possible sediment type (load, suspended and mixed) which were originated in desintegration processes. The sediment type domination, which was produced from watershed, was confirmed from granulometric composition of sediment in experimental watersteams. The synthesis of results of this analyses is presented with map of potenatial source of sediments from experimental watersheds.

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.

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.

The present paper cites results of studying phytoplankton in the Grosnica Water Reservoir, Serbia (Yugoslavia). Seasonal investigations during 1997 and 1998 enabled us to establish composition and structure of the phytoplankton community, quality of the lake's water, and its trophic status. During the period of investigation, the phytoplankton community was characterized by forms of Cyanophyta, Pyrrophyta, Chrysophyta, Bacillariophyta, Euglenophyta and Chlorophyta. Qualitative analysis indicated that algae of the divisions Bacillariophyta and Chlorophyta are dominant in the phytoplankton, while saprobiological analysis using bioindicatory algal species showed that water of the Grosnica Water Reservoir during the given period was of the 1st and 2nd quality class.

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.

It has been done the analysis of the physical and chemical characteristics of the water from two households in the village Berkovac in the foot of the mountain Maljen, Serbia (Yugoslavia). These households are supplying from two different springs. The water from the spring "Dobracinovica izvor" is contaminated and it is not for use, but the quality of the water from the hill Kulica is satisfactory. Both of them belong to the group of cold mineral waters.

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.