Management of aquatic ecosystems and planning of their protection needs good knowledge about their conditions. Mathematical modeling becomes one of the basic things in that processes. Last decades was attain important progress in quality at the beginning relative modest models of aquatic ecosystems. During the analysis of existing experiences to forced a conclusion that a quality model in one's own structures needs proportional representation of hydrodinamic and ecology background.

The sampling of Crnojevica river has been carried out, because of estimation the correlation between main water quality parameters and precipitation impacts, as well as adequate hydrological parameters. An appropriate dynamic sampling has been applied. Continuous pollution of river water has been confirmed, as well as source of the pollution. It is estimated strong correlation of water quality parameters from precipitation quantity and water level, especially for sanitary pollution. Change of quality parameters value is discrete and accidental.

In recent works enzymatic phosphatase activity state as a new potential good indicator for water saprobity and trophic state in water. On water reservoir 'Grliste' reinstated monitoring on the base physico-chemical, microbiological and biological analysis from beginning works water factory 1990 but, from 1998 use of this new biochemical method in monitoring as reliable additional indicator in fast preliminary water quality and the ecophysiological state of water. According to the results obtained for index of phosphatase activity (IFA) (Matavulj, 1986) water of 'Grliste' water accumulation belongs to category 3-A (polluted water).

Water quality studies of the Danube river in Belgrade region (Serbia and Montenegro) were performed at five locations, in June and September, 2003. Results of the qualitative, quantitative and saprobiological analyses of plankton and macrozoobenthic communities were used for the water quality assessment and the categorization of the watercourse examined. The bioindicator analysis points to the presence of mild organic pollution, water quality varying between the 2nd and 3rd class.

The paper presents the results of investigation of benthic algae of the river Rasina. During April, 2001, it was determined 110 algal taxa from the divisions Cyanophyta, Bacillariophyta and Chlorophyta, which indicate the high biodiversity of algae in this river. With 97 algal taxa, Bacillariophyta is dominant. The community of benthic algae is typical for this kind of aquatic ecosystem during the spring period. Great number of algal bioindicators of highly polluted water indicates the presence of high concentration of organic compounds in this aquatic ecosystem.

Pilot screening of sediment quality on selected stretches of HS DTD and transboundary water bodies in Vojvodina Province (Serbia and Montenegro) was set as an objective of this paper. The results of sediment toxicity tests indicated the necessity for remedial activities of the following stretches: DTD Vrbas - Bezdan - sampling site Vrbas - Canal Banatska Palanka - Novi Becej - sampling site Kajtasovo and Begej - sampling sites Klek and Stajicevo.

Investigations of phytoplankton in the Montenegrin coastal sea through summer (June, July, August) 2003 are described in this paper. They represent continuation from the previous years, and especially from 2001 and 2002. Maximum microphytoplankton quantity is found in the area of the bay (Kotor Bay) during June 3.9 x 10**6 cell/cubic dm, with the dominance of Nitzschia delicatissima (99%). This species was found with high percentage (more than 50%) during July and August, too. Leptocylindrus minimus and Skeletonema costatum, which were dominant in the previous period, through this year were slightly presented. In the area outside the Bay of Boka Kotorska, microphytoplankton was presented with quantities cell between 10**3 and 10**5 cell/cubic dm. Mean values of microphytoplankton in the area of the Boka Kotorska Bay were in 2003 year 4.6 times higher than outside the Bay. The same ratio was found for nanophytoplankton, too.

The paper is concerned with the procedures of treatment of wastewaters from sugar-processing plants. A short survey is given of both the aerobic and anaerobic procedures with a special regard of the possibility of recirculating the treated wastewaters. Data are presented for treatment of wastewaters originated from sugar-processing plants by the active sludge procedure carried out on a laboratory scale. It was concluded that thus purified water, after final membrane treatment, could be recirculated to the production process.

In this study, the possibility of application of agricultural lignocellulosic waste materials as adsorbents of different heavy metals ions from water was investigated. As adsorbents, wastes of widely cultivated plant cultures in our country were used. They were wheat straw, cornstalk, corn cob and soybean straw. These materials were showed as good adsorbents in most cases. But, leaching of organic matters from them during adsorption was observed. It was unfavourable. Because of that, adsorbents washed and dried. After that leaching of organic matters was significantly decreased, but also adsorption efficiencies slightly decreased, too.

Advancement in microbiology reveals new potentially pathogenic water borne microorganisms. Because of inconvenient water works, World Health Organization and legislators necessarily standardize guidelines and codes for potable water examination. Water works with safe water treatments and distribution systems obey the rules of routine control, and that is why they do not recognize more sophisticated sides of microbiological water quality. From that point of view, poorly studied slow growing chemoorganotrophic bacteria resistent to environmental conditions are interesting.