Important differences in the structure of fauna communities of their deepest parts of benthos were found in the investigation of several water reservoirs (Gruza, Grosnica, Barije, Bor, Vlasina and Medjuvrsje) on the territory of Serbia (Yugoslavia) lasting several years. The pronounced alterations of the structure are in the correlation to the pronounced degree of eutrofication was also established according to other indicators, above all according to the concentration of biogenic salts and the amount of organic substances. Characteristic group and taxa of the fauna of benthos which point to certain level of eutrophications were separated.

Monthly sampling in the Grosnica water reservoir near Kragujevac, Serbia (Yugoslavia), was carried out in the period October 1996 - September 1998. Comparison of the results with those obtained in 1950-1952 revealed changes in the qualitative and the quantitative composition of zooplankton. The presence of a considerably greater number of species was recorded, including some that were registered for the first time in this reservoir and which represent a very significant component in the dynamics of its zooplankton. A multi-fold increase of zooplankton production was also observed. The number of recorded species fluctuated from 26 in the winter to 59 in the summer. Average total abundance of zooplankton ranged from 100.7 ind./l (late spring to 2508.6 ind./l (summer). The results indicate an intensive process of eutrophication in the Grosnica water reservoir, the oldest artificial lake in the this part of Yugoslavia.

The present paper cites results of studying phytoplankton in the Grosnica Water Reservoir, Serbia (Yugoslavia). Seasonal investigations during 1997 and 1998 enabled us to establish composition and structure of the phytoplankton community, quality of the lake's water, and its trophic status. During the period of investigation, the phytoplankton community was characterized by forms of Cyanophyta, Pyrrophyta, Chrysophyta, Bacillariophyta, Euglenophyta and Chlorophyta. Qualitative analysis indicated that algae of the divisions Bacillariophyta and Chlorophyta are dominant in the phytoplankton, while saprobiological analysis using bioindicatory algal species showed that water of the Grosnica Water Reservoir during the given period was of the 1st and 2nd quality class.