The Hirudinea species were collected from various running waters and lakes in Turkey. The sampling sites were located on YeAYilA +/- rmak River, streams in Yedigoller National Park, Buyuk Menderes River, Lake BeyAYehir, Lake IAYA +/- klA +/-, Karamuk Marsh and Karadut Spring of AcA +/- gol Lake. Recorded species were evaluated with physicochemical variables such as temperature, pH, dissolved oxygen, conductivity, nitrite nitrogen, nitrate nitrogen, ammonium nitrogen, orthophosphate phosphorus and substratum structure. In this study, eight Hirudinea species were determined. These are Helobdella stagnalis, Erpobdella octoculata, Erpobdella testacea, Erpobdella vilnensis, Dina stschegolewi, Hirudo verbana, Limnatis nilotica, Haemopis sanguisuga. The relationships between leech species and water quality variables were assessed with canonical correspondence analysis. The results show that leech species which are found in the present study are able to live in different saprobic levels in streams and trophic levels in lakes, but they usually prefer polluted environments. Knowledge of ecological characteristics of leech species must be improved to use them in water quality assessment much more effectively.