This study was conducted in a portion of the Tunca River within Turkey's borders. Its aim is to investigate possible differences in Oligochaeta colonization in different leaf packages and to determine the impact of leaf litter on the distribution of aquatic oligochaetes. Simultaneously, the reasons for differences in Oligochaeta species colonization were investigated, and it was concluded that these differences were linked to the mesohabitat structure. Three stations were selected on the river for the study. Leaves from five different trees in the vicinity of these stations were gathered, packaged, and thrown into the water. When packing leaves, a 20 kg sack of potatoes was used, and a total of 25 packs were placed in localities. In addition, Oligochaeta samples were collected between May and October 2012 using a hand net. A total of 79 samples were obtained in areas of six different mesohabitats: Platanus orientalis leaf litter, Ulmus leavis leaf litter, Morus alba leaf litter, Juglans regia leaf litter, Buxus sp. leaf litter, and hand net samples. In the mesohabitats sampled, 751 specimens were identified, among them of 17 taxa and nine genera belonging to the family Naididae. Principal components analysis revealed the first two axes explained 89.3% of the total variance of the data. Limnodrilus hoffmeisteri was associated with the J. regia leaf litter, and Psammoryctides albicola was associated with the P. orientalis leaf litter. Most species determined demonstrated apparent affinity with the Buxus sp. leaf litter mesohabitats.