Lake ecosystems determined by trophic conditions, accurately defined Ecological status of protected area. Trophic condition of water of Lake Skadar and two rivers, the inflow Moraca and the outflow Bojana was described via plankton data considering abundance of phytoplankton, seasonal dynamics of organotrophs, cyanobacteria, total coliforms, plankton biodegrading potential and nitrogen fixing bacterioplankton. The trophic potential for phytoplankton growth has been detected in late autumn throughout September-November 2004, contrary to early summer June-July 2005, and adverse growth of bacterioplankton in May, June and September 2005, respectively. The results of quantitative analysis of coliforms showed good relation of Lake Skadar and Ada Bojana, contrary to similarities between Moraca River and Ada Bojana estimates in accordance with the Pantle-Buck index. Nevertheless, investigation pointed out Lake Skadar beta-mesosaprobic level and moderate self-purification rate. In evaluating trophic conditions the good ecological potential of protected area has been proposed.

In the year 2010 ichthyological research on some Vrbas River tributeries located on wider area of Banjaluka city (Bosnia and Herzegovina) was carried out and the occurrence of 14 fish species was recorded. On the basis of the occurrence and abundance of fish species indicators as limnosaprobic parameter, water quality of the analyzed watercourses variated from oligosaprobic to beta mesosaprobic (I and II class of bonity) with saprobic index from 1.27 for Švrakava River to 1.81 for Vrbanja River. The obtained results indicate that water quality of this Vrbas River watershed was on satisfactory level for multiple purposes (in order to sustain ichthyofauna diversity and production and as potential protected areas and spawning zone for some endangered domestic fish species).

In this work, the results of preliminary study of stomach content in brown trout (Salmo trutta L. 1758) of the Gradac in autumn are presented. The fishes were collected by the end of September of 2011 at three sampling sites along the course. A total of 12 fish specimens were examined. By examination of trout stomach content have been found members from macrozoobentho-groups – Trichoptera, Ephemeroptera, Diptera (fam. Ceratopogonidae), Oligochaeta, Coleoptera. At the same time, investigations of bottom fauna composition and structure have been done also. Our study showed that the diet of brown trout is dependent of bottom fauna availability and abundance.

The paper presents aquatic macroinvertebrate community at four investigated localities of the Gradac river. Sampling was carried out during 2003 and 2006. Community structure and composition, together with field data, were used to estimate the water quality status of the river. A total of 87 taxa have been recorded. Insects were found to be the most diverse component, especially Ephemeroptera. Insects were dominant in the regard of the quantitative structure of the community, as well. Recorded community indicates good water quality, ranged between oligosaprobic and beta-mesosaprobic status (1st-2nd class according national classification scheme).

The analysis of breaks and gaps frequences in the fish species Alburnus alburnus from different localities of rivers Kolubara, Sava and Danube, were showed the highest values that were above the presumed critical zone (3.0-3.5% of changes). At some of localities examined in May and October 2008, these values were much more elevated that the level of spontaneous changes normally seen in the controls in laboratory animals and in fish of relatively clean waters. Results that were obtained for these localities indicate to periodical or permanent contamination with genotoxic agents.

Jegricka water body is part of the Main Drainage Channel System. The whole length of Jegricka (65 km, catchment surface 60.380 ha) is located in south part of Backa, Vojvodina Province. This highly modified water flow has become protected area since 2005 due to its specific natural features - diversity and uniqueness of biotic features, especially for birds and plants. In July 2008 survey of freshwater macroinvertebrates was conducted in order to assess water quality and conservation potential according to biotic characteristics according to conservation criteria within SERCON (System for Evaluating Rivers for Conservation) method. The aim of this paper was to evaluate the importance of macroinvertebrates as indicators of conservation potential of Jegricka water using SERCON. Results of analyses of species composition of freshwater invertebrates fauna showed presence of 12 higher taxonomic groups. Within these groups, 23 families were present at eight RHS river sections along investigated part of Jegricka water body. Togheter with SERCON based conservation criteria for macroinvertebrate, two types of biotic indices Biological Monitoring Working Party (BMWP) and Average Score Per Taxon (ASPT) were calculated in order to assess water quality. Results of the survey showed that Jegricka water body belongs probably to moderately polluted water type according to biotic indices. Results of conservation criteria Naturaless showed that observed and expected faunas are similar. Low values of SERCON family richness criteria based on whole length of water body indicate that Jegricka has low conservation potential, and that adequate rehabilitation measures should be considered in the future.

This paper shows the results of research of some phytoplankton and saprobiological characteristics of water in reservoir Grliste and the flowing rivers during the period of January 2001 to December 2007. During this period of researching, phytoplankton community was characterized by forms of Bacillariophyta, Chlorophyta, Cyanophyta, Chrysophyta, Pyrrophyta and Euglenophyta. Saprobiological analyses using bioindicatory species of algae showed oligosaprobic and beta-mezosaprobic characteristics of water in the reservoir. The analyses showed the poor water quality of Lesovacka and Lenovacka rivers which flow in reservoir. This water was determined as beta-mezosaprobic and alfa-mezosaprobic type. The phytoplankton was characterized by forms of Bacillariophyta, Chlorophyta, Pyrrophyta and Euglenophyta.

During the field research of phytocenous characteristics of the Moravica river flow and the influence of anthropogenic pollution, hygrophilous ass, Salicetum albae-fragilis (willow grove-shrubs in moist habitats) which grows in the middle reaches of the Moavica, has been found. The community develops in the middle reaches and it indicates highly polluted waters. The aim of this paper is to establish phytocenous contents of the community and ecological conditions of the habitat (indicatives of water quality of the Moravica river) based on ecological index of vascular plants.

During 2005-2006 the seasonal researches were taken place aiming to investigate the influence of the urban waste water on the qualitative and quantitative structure of the community of macrozoobenthos in Gabrovacka river. For this purpose five sites were determined and the sampling of the macrozoobenthos was organized on the seasonal level using Surber net.

In the project Quality of Drinking Water of Banja Luka City, during 2007 the colony of zoobentos around the water factory is followed. The composition of colony is different in both season and horizontal profile. The quality of water in litoral area of river is much worse, because polluted water from ambiental settlement and that is indicated by major number of Tubificidae. During monitoring of the states there was a change of qualitative and quantitative composition of colony, also and the change of individual domination of taxons.