ABSTRACT
The presence of cyanobacteria [blue-green algae] is a significant indicator of water quality, having in mind that several genera have the quality of producing cyanotoxins, which are harmful to animals, plants and humans. Seven lakes in Vojvodina [Republic of Serbia] were examined in May and September 2007 for cyanobacterial presence and cyanotoxins content, Chl a concentration and index of phosphatase activity as the indicators of water quality. In the spring period, cyanobacteria species were not dominant in only 2 of 14 water samples. Microcystins were detected in all of the lakes examined. The concentrations of microcystins ranged from 6.66 Micro g/L [Provala Lake] to 199.9 and 238 Micro g/L [Palic and Ludas Lake respectively]. The investigations conducted on 7 water ecosystems in Vojvodina, regarding the basic parameters of eutrophication, Chl a concentration and phosphatase activity index, have rendered the examined ecosystems immensely endangered due to significant water quality deterioration. It was determined that the intensification of eutrophication processes has been linked to the increased presence and abundance of cyanobacteria as well as significant toxin production