Water quality studies of the Danube river in Belgrade region (Serbia and Montenegro) were performed at five locations, in June and September, 2003. Results of the qualitative, quantitative and saprobiological analyses of plankton and macrozoobenthic communities were used for the water quality assessment and the categorization of the watercourse examined. The bioindicator analysis points to the presence of mild organic pollution, water quality varying between the 2nd and 3rd class.

The paper presents the results of investigation of benthic algae of the river Rasina. During April, 2001, it was determined 110 algal taxa from the divisions Cyanophyta, Bacillariophyta and Chlorophyta, which indicate the high biodiversity of algae in this river. With 97 algal taxa, Bacillariophyta is dominant. The community of benthic algae is typical for this kind of aquatic ecosystem during the spring period. Great number of algal bioindicators of highly polluted water indicates the presence of high concentration of organic compounds in this aquatic ecosystem.

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.

The paper presents the results of the water quality studies of the Sava river in Belgrade region (Serbia and Montenegro). The investigations were performed in June and September, 2003. The sampling area covered five locations along the 61.5 km of the river course. Studies included the qualitative, quantitative and saprobiological investigations of plankton and macrozoobenthic communities. The bioindicator analysis points to the presence of mild organic pollution indicating thus 2nd and 3rd-2nd class of water quality.

In this paper we have presented the results of the investigations of phytoplankton carried out in the river Old Begey, from April 2003 till February 2004. The presence of 116 algal taxa of which 10 Cyanobacteria, 20 Euglenophyta, 50 Bacillariophyceae, 3 Chrysophyceae, 30 Chlorophyta and 3 Dinophyta was recorded. In the river Old Begey some rarer brackish species Entomoneis alata and Bacillaria paradoxa have also been found. The index of saprobity given on the basis of Pantle-Buck method indicated that the quality of water of the river Old begey belonged to beta-alfa-mesosaprobic category.