N,N-diethyl-m-toluamide (DEET) is a widely used insect repellent and a very effective pesticide applied to skin or clothing to remove insects or rodents. It is also among personal care products. DEET can be toxic to birds, fishes and aquatic invertebrates. For this reason, determination of concentrations in surface waters is very important for living things that live in or feed in aquatic environments. This work was carried out in Ivriz, Ayranci, Godet, Sucullu, Uluborlu, Kozan, Mehmetli, Seyhan Dam Lakes, Golbasi, Azapli, Inekli Lakes and Ceyhan River in the Middle South of Turkey. During this study, DEET was detected in all surface water samples taken from lakes and Ceyhan River and the obtained average DEET concentrations are ranged from 0.57 to 80.10 ng/l. The highest concentration obtained was found in the Ceyhan River in summer. When the averages of DEET concentrations are listed, the first three are Ceyhan River, Golbasi Lake and Seyhan Dam Lake, respectively. Higher DEET concentrations were found in summer in most lakes and Ceyhan River. Despite the fact that the measured DEET concentrations in surface waters are well below the acute effect concentrations, but it is not known exactly how their effects will be when DEET behave with the other pollutants.