State Of Phytoplankton Community In The Bulgarian And Macedonian Lakes Daniela Petrova, Suzana Patceva, Vasa Mitic, Galina Shtereva, Dimitar Gerdzhikov Institute of Fisheries and Aquaculture Varna, Bulgaria Abstract For the Balkan Peninsula Lakes ecosystems the phenomenon of water quality deterioration has been evident since the early 1980-s. These lakes are one of the hot spots along the Bulgarian Black Sea coastal zone and coastal zone in Macedonia. Its ecological state is strongly influenced by the process of anthropogenic presses. Along the lake coast are located many sources of pollution such as rivers, ports, chemical industry. It has significantly influenced fishing, aquaculture, tourism and caused enormous economic losses. The paper present a results of investigations of lakes with different trophic status in Bulgaria (Varna and Beloslav Lakes) and Macedonia (Lakes Ohrid and Prespa). Seasonal and inter – annual variability of species composition, predominating groups, abundance and biomass of microalgae in both areas are analysed. Considering the hydrological connection of Lakes Ohrid and Prespa, one of the oldest lakes on earth, comparative investigations were carried out on the basic trophic parameters with particular attention to the phytoplankton community as the most sensitive indicator of changes on trophic conditions in the lakes. The goal of this research was to obtain information about the rate of change in their trophic state as a consequence of the anthropogenic influence and decline in the water level of Lakes. Keywords: Varna Lake, Lake Ohrid, Lake Prespa, phytoplankton, eutrophication, Introduction Varna and Beloslav lakes are under constant influence of industrial agricultural and transport activities. The influence on anthropogenic impact and the consequences in lake’s ecosystem were discussed in various publications(Petrova,V.,1961; Velikova,V.,Petrova,D.,1999; Velikova, V., Moncheva, S., Petrova, D. ,1999; Velikova et al., 2001; Velikova, V., Petrova, D., 2003; Moncheva, S., 1991;Petrova,D. et al., 2004). For the last few decades was informed not only about the hydrochemical and hydrophysical changes but also about the changes in planktonic community( Velikova, V.,Petrova,D., 1999; Moncheva, S, et al.,1995; Petrova,D. et al., 2004;). The Varna lake is the biggest at the Bulgarian coast. Full amount of two lakes is 165x103¬¼ and their area is equal 17,4 km. Lakes Ohrid and Prespa are one of the oldest lakes in the world with an estimated age above 3 million years. They are situated in south-eastern Europe and they are the biggest lakes in Macedonia. Lake Ohrid covers an area of 358.2 km 2 , it has a shoreline of 87.5 km, a maximum length of 30.8 km and a maximum width of 14.8 km. The lake has a maximum depth of 289 m. Lake Prespa covers an area of 274 km 2 , it has a shoreline of 87.5 km, a maximum length of about 28 km and a maximum width of 17 km. The lake has a maximum depth of 54 m but today due to water level declination it estimated on 48 m.. Lake Prespa, situated at an altitude of about 849 m asl lies about 160 m higher than Lake Ohrid. The main purpose of the following feature is to describe the current condition of the different by the status of Balkan lakes assessing their phytoplankton communities as the indicator Lake Ohrid is oligotrophic lake but in the last several decades was not exempted from the general tendency of the enhanced anthropogenic influence. Growth population, more intensive human activity in the domain of industry, tourism, fishery, agriculture and forestry more and more endangered natural worth of Lake Ohrid. Especially large negative impact on the littoral zone of Lake Ohrid have bigger tributaries.