In this project, the swimming performance of Tarek (Alburnus tarichi), which is the unique fish species that can survive naturally in Van Lake as a soda lake and performs compulsory reproduction migration to freshwater, has been investigated taking into consideration the effects of various factors. This endemic species has economical, ecological and touristic importance in terms of its region. Breeding migration of this species is the most important activity to maintain its generation. Because Tarek can only spawn in freshwaters, it enters freshwater sources from Spring to reproduce and performs an intense swimming activity. Despite all these conditions, there has been no investigation in the literature to determine swimming performance of this species. In this study, the swimming performances of Tarek individuals were investigated in the swimming performance test contrivance, which has composed with the same characteristics as Lake Van and the freshwater environments. It was possible to determine critical swimming speeds (Ucrit) at different water temperatures (5-10-15-20 °C) and in environments with different chemical structures. In addition, using also individuals of different height-weight and gender groups (since the individuals were collected from the nature it is already a necessity) in the experiments, also effects of these factors on swimming performance were determined. It has been found that the critical swimming speeds of fish swimming in freshwater environment is higher than that swimming in Van Lake water environment for every temperature value. It also came to the conclusion that individuals who have not reproduced yet have a superior swimming performance than those who have already laid their eggs. Statistically the relative critical swimming speed (rUcrit) value (avarage of all water temperature and environments) of males were found to be higher than females (5.16 Total length.s-1 – 4.66 Total length.s-1) although Ucrit values were not different (107.17 cm.s-1 – 103.68 cm.s-1). The average Ucrit and rUcrit values of Tarek were calculated for the water temperatures of 5-10-15-20 °C respectively as 71.29 cm.s-1 – 3.29 TL.s-1, 92.65 cm.s-1 – 4.23 TL.s-1, 113.046 cm.s-1 – 5.35 TL.s-1 and 119.138 cm.s-1 – 5.56 TL.s-1 (general average: 99.03 cm.s-1 – 4.61 TL.s-1) in Van Lake water environment and 86.58 cm.s-1 – 4.072 TL.s-1, 105.8 cm.s-1 – 4.88 TL.s-1, 121.86 cm.s-1 – 5.6 TL.s-1 and 131.88 cm.s-1 – 6.15 TL.s-1 (general average: 111.53 cm.s-1 – 5.17 TL.s-1) in freshwater environment