The centric diatoms of different river basins in Marmara and Aegean regions, Turkey (Akarcay, Buyuk Menderes, Gediz, Marmara, Porsuk, Sakarya and Susurluk river basins) Cüneyd Nadir Solak1,2*, Maxim Kulikovskiy3, Irina KUZNETSOVA3 1 Department of Biology, Arts and Science Faculty, Dumlupınar University, Kütahya, 43100 – TURKEY 2 Department of Palaeoceanology, Institute of Marine Sciences, University of Szczecin, ul. Mickiewicza 18, Szczecin, 70-383 – POLAND 3 Department of Algology, I. D. Papanin Institute for Biology of Inland Waters, Russian Academy of Sciences, Yaroslavl, Nekouz, Borok, 152742 – RUSSIA Abstract: Investigation of benthic diatoms is recommended by the Water Framework Directives (Water Framework Directive, European Parliament 2000 directive, 2000/60/EC). They are considered key organisms in ecological quality analyses of water courses and have been applied in Europe (Ács et al., 2004). Although Turkey has great potential of inland water relatively is known about the flora. It is necessary to study the flora of Turkey as part of the biological monitoring requested by the European Water Framework Diective and also the investigation of the freshwater algal flora. This study includes some river basins in Marmara and Aegean Regions (Akarçay-0.49 billion m3, Büyük Menderes-3.03 billion m3, Gediz-1.95 billion m3, Marmara-1.33 billion m3, Susurluk-5.43 billion m3 and Sakarya-6.40 billion m3). Among the river basins, Akarçay and Gediz river basins are some of the smallest river basins and rarely investigated basins by diatoms in Turkey. In this study, 134 stations were investigated including Akarçay, Marmara, Susurluk, Sakarya, Gediz, Büyük Menderes river basins in Marmara and Aegean Regions and totally 15 centric taxa were identified. According to the results, Aulacoseira ambigua and A. granulata, Cyclotella atomus were very common in Marmara river basin in Yalova streams. Conticribra weissflogii and Handmannia balatonis were only found in Sakarya river basin in Kütahya streams. Stephanodiscus invisitatus was only found in Susurluk river basin; Orthoseira dendroteres in Susurluk river basin while Cyclotella meneghiniana and Melosira varians were very comon in all river basins. Keyword: Aegean region, centric diatoms, Marmara region.