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.

Oxygen aspect of water pollution of Skadar lake, Montenegro (Yugoslavia) is considered in this paper. Water analysis data in the period of 1991-1998 were used to establish relevant parameters, oxygen saturation (%O2), and five day biochemical demind (BPK5). Those data were supplied by Hydrometeorological Institute in Podgorica, Montenegro (Yugoslavia). Measurements were taken from three places in northern part of Skadar lake, where the increased water pollution is expected, and from southeastern part of the lake, out of source of pollution directly influence. According to results from this research, there is close relation between water pollution and oxygen water balance. Parts of the Skadar lake with low water circulation are especialy susceptible (place Kamenik). In the 1991-1995 period, this phenomena is manifested with variation depending of the chosen area and year. After some improvement of water quality in the 1996-1997 period, there is noticeable increase of water pollution in 1998 at all places. Supersaturation was identified by the percentage of O2 in Skadar lake area at whole.

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.

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.

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.

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.