The aim of this study was to determine the current fish fauna and their distribution rates in Lake Sapanca and its tributaries. For this purpose, standard benthic and pelagic nets were used in the lake and a portable electroshock device was used in the streams. As a result of the sampling carried out in two different seasons, wet and dry periods, the presence of 26 species from 14 families was determined and the abundance values for many species were higher in the wet season. In terms of species diversity, the Leuciscidae family ranked first with 9 species, while the Gobiidae family was represented by 4 species, the Clupeidae family by 2 species and the remaining 11 families were represented by one species each. In terms of individual density, Rhodeus amarus was the most dominant fish in both lake and streams (78.1% lake; 28.3% stream). In the lake, Blicca bjoerkna, Clupeonella cultriventris, and Atherina boyeri were the most abundant species after R. amarus (7.2%, 3.2% and 3.2%, respectively). An important finding of the study was that there were almost no individuals of Silurus glanis, Esox lucius, and Cyprinus carpio (4, 8 and 1 individuals, respectively), which are species of high commercial value in the lake. In addition, the fact that Carassius gibelio, one of the invasive species reported in previous studies, was not found in the lake is very pleasing in terms of lake biodiversity. In addition, Leucaspius delineatus, caught in both seasons, was identified from the lake basin for the first time.