Low flows are a good measure of the waste water recipient self-purification capability. The regional statistical analysis is an objective way of assessment of the required low flows. This paper presents the principles and key phases of the regional statistical analysis. The advantages of this method are a reduction of the outliers influence and the assessment of low flows on ungauged streams and stream profiles. The method is illustrated with the results obtained by the required low flows regional statistical analysis in Serbia (Yugoslavia) with 59 hydrological gauge stations in the scope, which data has the same length of 39 years, from the year 1956 to 1994.

Spectrophotometric method for determination of inorganic phosphate liberated in hydrolysis of ATP catalyzed by ATPase was modified in order to obtain faster procedure, which could also be used in none laboratory conditions. The modification has some advantages compared to the most used Pennial method: a) the reagents are stable for several months; b) the 45 min procedure of phosphomolibdate extraction by isobutanole-benzene is ommited, and the method is not dangerous for the analyst; c) color develops after 20 min. The method was tested on the determination of inorganic phosphate in the presence of cadmium nitrate as inhibitor of ATPase activity. The results were compared to the results obtained by Pennial method. The results obtained have shown some good agreements.

Problems encountered in evaluating surface water quality arise from the requirements of relevant regulations that these evaluations should be made in the last favourable hydrologic conditions during design flow rate (required minimum flow). However, the major part of measurements of water quality parameters is not performed under such conditions and the result must be corrected for the conditions under required minimum flow. Two possible approaches to solving this problem are presented in this paper and explained using an example of the Juzna Morava river basin up to the Station Korvingrad, Serbia (Yugoslavia). This basin is unhomogeneous regarding its hydrologic characteristics and mass flow of pollutants. The results of analysis are presented in the cartography form using the GIS technology.

Owing to the habit of most of Yugoslavs to prepare coffee without filtering, the large part of used coffee comes to recipients. In this paper, the influence of coffee deposits reaching recipients in Yugoslavia is analyzed. Results of laboratory examination of the biodegradability and kinetic of biodegradability of coffee deposits are also presented.

In this paper, the results of statistical analysis of then years water quality data of Tamis river at the Romanian-Yugoslav border ("Jasa Tomic" Control Station) are presented. Following changes of analyzed water quality parameters at the Romanian-Yugoslav border a strong trend of deterioration has been observed during analyzed period. Because of periodical accidentally high organic content (COD, BOD) and concentration of ammonia and organic nitrogen in river water, it is concluded that upstream discharging of farm waste waters was the main reason of deterioration of water quality along the Yugoslav part of Tamis river.

In this investigation the applied method for lead determination in traces, from 10E-6 - 10E-10 mol/cubic dm, was Potentiometric Stripping Analysis (PSA). The main attribute of this method is possibility to detect very low metal concentrations. The investigation results of level concentration of lead into the top, natural and atmospheric water from some towns of Serbia (Yugoslavia), including city of Belgrade, are given. The investigation was carried out in some towns of Serbia (Yugoslavia), including city of Belgrade, during the 1994-1995.

The experiment was performed on marine Teleost Serranus scriba with lower concentrations of lindane then MPC (due to our valid law). The aim of this study was to find the effects of lindane to fish activities connected with nutrition. This motive is among the strongest. It includes parameters as: number of fish movements in the presence of prey or without it and the number of onslaughts to the prey during one hour. The results have shown that the increasing of lindane concentration caused considerable decreasing and even complete cessation of activity. Interest for prey and decreasing activity of predators in the presence of prey (typical for Serranus - as a fish of prey and the hunter) endures till the moment of convulsion.

MPI - Metal Pollution Index is being proposed with an aim improving the freshwater pollution control, monitoring and classification based on fish metal body burden. This is a simple mathematical model which enables presentation of Cd, Pb, Cu, Zn and Al fish liver concentration as a single value. After thorough studies of bioaccumulation, biomagnification and tissue distribution patterns, liver of Carassius auratus gibelio has been chosen as sentinel organ. Normal distribution and biological variation assessment is being achieved by using normalizers - reference values (liver concentrations of selected elements in fish from reference sites Vruje and Moharac micro water reservoirs, Serbia (Yugoslavia)). Selected representative sites have been evaluated according to new classification of freshwater ecosystem based on MPI values.

In this paper we have pointed out the hydrogeological condition in the catchment area of the Jablanica river in the south Serbia (Yugoslavia). The two units are separately presented here. The first one is mountainous part of the catchment area upstream of the gaging station of Lebane and the second one is the part of the terrain in the plain down stream to the river mounth near Pecenjevac. The hydrogeological characteristics of the two mentioned regions are given to explain the reasons of existing the constant flow of the Jablanica to Lebane and its disappearing course in the period of recession in the plain downstream. The quality of water in the Jablanica river at Lebane is good. Down stream of this gaging station the waste water collector flows into the river. In the part of recession period the ratio between them is unfavourable. We have also discussed the quality of water at the gaging station of Pecenjevac and pointed out the function of sandy-gravel deposits in the process of natural purification of the Jablanica flow.