The distribution and frequency of Ulva , a cosmopolitan genus, in aquatic systems are increasingly expanding due to global warming and anthropogenic influences. In contrast to their widespread distribution in marine environments, information on their ecology and distribution in freshwater habitats remains limited. In recent years, a growing number of studies have focused on the distribution of the genus Ulva in freshwater habitats. This study aimed to provide the first record of Ulva pilifera (Kützing) Škaloud et Leliaert from the freshwaters of Türkiye. Algal samples were collected from the Killiközü Stream in Yozgat Province in August 2022. Based on morphological examinations, the algal samples were identified as having a bright green, convoluted, fragile, tubular, and calcified structure, with sparsely branched thalli measuring 0.18–0.53 × 2.06–12.44 cm. The dimensions of single-row apical cells, which appear in different shapes, were 6.92–8.97 × 9.49–17.09 µm. The mean dimensions of the polygonal cells were 10.98 × 15.41 µm, and the circumference ranged from 36.51 to 52.72 µm. The cell sizes in mature thalli were 8.04–14.07 µm × 8.23–21.84 µm. The average thickness of the cell wall was measured to be 1.55 µm, with a range of 0.5 µm to 2.06 µm. The pyrenoid diameter of the species, which possessed 2 or 3 (rarely 1 to 4) pyrenoids, ranged from 1.26 to 4.23 µm. The collected algae samples were identified as U. pilifera based on their microscopic features. This finding contributes to the understanding of regional flora, providing a scientific basis for future monitoring studies.