During several years of hydrobiological investigation of the Zapadna Morava river the Medjuvrsje and Stancici localities stood out; the most favourable water quality was registered with the Medjuvrsje reservoir (being constantly of the class 2), whilst, according to all the data obtained over the years, water quality of the Zapadna Morava at Stancici locality was the worts. The Medjuvrsje reservoir is in stable eutrophic phase. The saprobic index value points to a certain water quality improvement. Floristic diversity in the locality of Stancici increased over the years. An increase in the percental share of the oligosaprobity indicator indicates a certain organic load decrease and an improving water quality trend was recorded as indicated by lower saprobic index values.

Nitrogen and phosphorus contents in water, sediment and shoots of Phragmites communis Trin, and Typha latifolia L., as possible indicators of trophic state were used in the area of the Bardaca fish-pond. The results of total nitrogen and phosphorus contents during growing season indicate the hypertrophic state of waters in all locations.

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).

Thermal waters represent an unused natural potential of Serbia. A possible way of utilizing this resource is to carry out the initiative that has been underway over the past several years to use certain thermal waters for the rearing of some allochthnous thermophilic fish species, the most famous among them being the group Tilapia (fam. Cichlidae), authochthonous in Africa and Asia. The analysis of basic physico-chemical properties of the Ovcar Banja (Ovcar Spa) thermal waters (the bed of the Zapadna Morava river, Western Serbia) indicates the possibility of their utilization for this purpose.

In this paper, there were discussed the results of ecological investigation of the Montenerin part of the Adriatic sea during the period 1996-2003. Evaluation of the sea-water quality was done in the coastal sea. The importance of multiannual ecological investigations was emphasized, too.

The aim of this study was to determine the content of heavy metals, cadmium and lead, in drinking water, spring and well water from rural part of south Serbia, as in water of river Jablanica and in the top water. The content of cadmium and lead, a very toxic metals, were studied simulataneously by potentiometric stripping analysis (PSA) in water samples using thin mercury film electrode, as a working electrode, by standard addition method in the presence of supporting electrolyte. The results of content of examined heavy metals obtained in examined water samples by PSA method, are compared with results obtained by using AAS and GF-AAS spectrometry.

The work considers the effect of the ozonization process on the change of contents of natural organic matter (NOM) and formation of byproducts in the groundwater pretreated by preozonation (2.0 g O3/cubic m) and coagulation with polyaluminium-chlorosulfate (5 and 10 g Al/cubuc m). Experiments were carried out on a semi-industrial plant of capacity of 2 cubic m/h, using groundwater with a high content of NOM (5.1 mg/l TOC). It was found that in the course of ozonization NOM content shows a decrease (18-64%), as well as the potential of formation of trihalomethanes, PFTHM (12-59%), whereas content of aldehydes increases by 3.0-7.7 microgram/l, depending on the water pretreatment and applied ozone dose. It was found correlation between specific aldehyde content and decrease of the specific PFTHM (r=0.815-0.998).

New type of ozone generator based on barrier discharge was applied for removal of phenol from water under laboratory conditions. Three water samples with initial concentration of phenol of 6.0 mg/L were studied. In the experiment with distilled water containing phenol, 98.9% of phenol was removed (93.3% during the ozonization). Under similar conditions two different water samples from river Danube were used. In these cases, 76.7% and 80.0% of phenol were removed, respectively. In all experiments, water samples containing phenol passed only once through the ozonizer. It is reasonable to assume that better purification could be obtained with several passes of water through ozonizer and/or by optimization of the process (adjusting concentration of ozone, ozonization time, water flow, etc.).

The diffusion of erosive processes in Serbia and frequency of torrential floods are the factors of degradation of environment. Communities in Serbia are obliged to make Plans for announcement of erosive regions and for protection by torrential floods on water courses out of regular system of defense. An example of Belgrade is presented in this paper, where the Plans for announcement of erosive regions and defense by torrential floods were carried out. These documents are the basis for water protection and usage of natural resources on the concept of sustainability.

A new concept for the determination of reference low flows of natural watercourses - the guaranteed minimum - has recently been introduced into the water management practice. Appreciating the significance underlying the definition of low flows in all segments of water management (municipal and industrial water supply, wastewater discharge, irrigation, navigation, hydropower, water protection, etc.), the author believes that all aspects of the problem must duly be considered, examined and identified. The doubts and issues raised by the guaranteed minimum concept in the domain of random-probabilistic phenomena, such as river discharge, are discussed in the paper.