Compiling the available data collected over many years of research of Boka Kotorska Bay showed variability in terms of dynamics and abundance of phytoplankton organisms. The Boka Kotorska Bay is a relatively large (87 km2), semi-enclosed bay, located in the south-eastern part of the Adriatic Sea. In addition to human impact, significant inflow of freshwater from numerous karstic streams and submarine springs contributes to the unique ecological characteristics of the Bay, particularly in its inner part (the Kotor Bay). Based on the data presented for the Boka Kotorska Bay (the Kotor Bay) phytoplankton abundance reaches up to 107 cells/l. Diatoms are the phytoplankton group present throughout the year. In some researches conducted in the Boka Kotorska Bay diatoms abundance reaching up to 107 cells/l was recorded. Dominant species are typical of areas with higher eutrophication that prefer nutrient rich areas and are very good indicators of ecosystem conditions. Dinoflagellates are the second important group of microplankton, frequently found in the aquatorium of the Boka Kotorska Bay. Dinoflagellates are generally less represented than diatoms, both quantitatively and qualitatively. The maximal recorded phytoplankton values indicate changes that may lead to eutrophic conditions in the Bay ; however, it can be concluded that the Bay is still moderately trophic. According to the two trophic indices TRIX and Fp ratio natural eutrophication is still dominant over anthropogenic eutrophication in Boka Kotorska Bay.