A new locality for the invasive freshwater jellyfish (Craspedacusta sowerbii Lankester, 1880) was found during a study conducted in a mesotrophic dam lake (Ürkmez Reservoir, western Anatolia, Turkey). The study was focused on the limnological characteristics of the reservoir and conducted at monthly intervals between March 2014 and February 2015. Some limnological characteristics (physicochemical parameters, phytoplankton composition, and trophic status) of the investigating area are presented. In August and September 2014, jellyfish specimens were observed just beneath the surface (3-4 spec/m2). In the remaining period of the study, no jellyfish specimens were found in the limnetic zone of the reservoir. C. sowerbii has been rarely observed in Turkish freshwaters. The present record is the westernmost point of its distribution in Turkey. An overview of its distribution in South-Eastern Europe and the Middle East, and a map showing the actual distribution in the mentioned area was given.