This study was conducted between the years 2017-2018 in Lake Aygir within the borders of Adilcevaz district of Bitlis Province, in Lake Van Basin. Zebra Mussel (Dreissena polymorpha Pallas, 1771) was firstly discovered in Lake Van Basin via this study. The drinking water requirements of the settlements around are met from Lake Aygir. Zebra Mussel, which was firstly discovered during the diving organized for the clogged drinking water pipes, is thought to have arrived at the lake six years ago. In this study, 456 mussels were examined, and the height-weight relationships of the mussels were determined together with their distribution areas within the lake through dives. The biggest height and weight values were found as 37.73 mm and 5.96 g. As the conclusion of the regression analysis, it was also noted down that there was an exponential relationship between the heights and weights of the mussels, and they demonstrated an allometric growth accordingly. Furthermore, it was discovered that the mussels spreaded over an area of 0.4 km(2). Finally, some possible ecological effects of Zebra Mussels (Dreissena polymorpha Pallas, 1771) in Lake Aygir and Lake Van Basin were evaluated, and some suggestions were made as solutions to the problem.