According to the plans, the town of Gacko tends to be water supplied from the water reservoir Vrba located at the river Vrba. About 150 to 200 m away is located ash basin. All ash basin area is oriented to the water reservoir and leaking water going directly to the water reservoir. The leaking water has high pH value, alkalinity, high content of sodium, potassium and sulphates. There are some heavy metals, but their concentrations are not significant. The influence of those contaminated water on the lake water quality is only little evident because of the high dilution rate.

Man-made lakes cause direct and indirect changes in environmental conditions downstream of the water reservoir. Management must consider these water quality and environmental effects as well as uses of the river below the water reservoir.

Eutrophication is one of the main problems of water deterioration in accumulation lakes. Phosphorus is considered as the key factor for eutrophication of lacustrine water. Its concentration in lakes originates from external input and the emission from the sediment. It was necessary to determine the substrates of phosphorus by sequential extraction in order to determine the dynamics and bioavailability of phosphorus. On the basis of results obtained the proposals for the preparation of land were made in order to minimise the input of phosphorus.

Water samples for chemical and microbiological analyses as well as material of the water community to be considered in the assessment of qualitative and quantitative composition of phyto- and zooplankton, and bottom fauna were take on 30 May 2001 at two profiles. Judging by the most of the analyzed chemical parameters, with the exception of BOD5 and oxygen saturation values indicating class 2, water of the Bovan lake accumulation belongs to the 1st class of water quality. According to the presence of heterotrophic bacteria, water was characterized as class 1-2 (after Kohl). Also, 6 groups of phyto- and 4 groups of zooplankton were recorded. Relative abundance and qualitative composition values of plankton show that saprobic index ranged from 1.54 to 1.98 pointing out oligo-beta, namely beta-mesosaprobic character of the accumulation. Saprobic index when oligochaetes were considered amounted up to 3.6 (alfa-mesosaprobic water).

According to the Programme of systematic examination of surface water quality of the Republic Hydrometeorological Service of Serbia the examinations of Medjuvrsje water reservoir have been carried out during October 2002 and August 2003. The examinations have been carried out at the dam, in central part and at the entrance of the water reservoir, on three depths. This paper shows the results on phytoplankton composition, chemicophysical properties and the trophic status of water reservoir. The qualitative analysis of the phytoplankton shows the presence of 96 taxa from six divisions of algae. Following the standard of Swedish Agency for Environmental Protection, the high concentrations of primary nutrients belong to the fifth class, by the categorization. According to OECD classification trophic status of water reservoir may be characterized as eutrophic and hypereutrophic.

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).

The examined period is characterized by small floristic variety and well advanced eutrophication process. By the phytoplankton qualitative analysis it has been noted the domination of Bacillariophyta algal division. The values of density on phytoplankton population and their biomass show the domination of bluegreen algae, before each other, that of the species Gomphosphaeria lacustris Chod. As the consequence of the eutrophication, these algae develop intensively, up to the degree of water blossoming. The very high concentrations of the primary and secondary nutrients have also been noted. The trophic status of the reservoir on the basis of OECD classification can be defined as eutrophic.

Faculty of Science, University of Kragujevac (Serbia, Serbia and Montenegro), has developed SeLar Information System (Serbian Lake and Reservoirs Information System) which provides all the information of Serbian lakes and water reservoirs. Information system is needed for transfer of knowledge and informations, cooperation among participant in management and support of sustainable using of water resources. The paper presents the basic system components and some applications examples.

Consequently to eutrophication, from the beginning of July to the end of November there was a water bloom in reservoir Celije generated by three cyanobacterial species. Monitoring of that phenomenon indicates that cyanobacteria have become phytoplanktonic dominant residents in the course of significant part of the year.