Koycegiz Lagoon System (KLS) in the southwestern part of Turkey have tectonic origin. Surface area of the Lagoon Lake is 5,500 ha. The basin of the System is covered by the agricultural areas and small settlements. System is rich in terms of biological resources. In this region the most important activities are tourism and fisheries. The water, sediment, plankton, and fish samples were collected and analyzed for organochlorine pesticide residues in this system. Organochlorine pesticide residues were not detected in water and plankton samples. Residues of 5 organochlorine pesticides were found in sediment samples, while 7 organochlorine pesticides were found in fish samples.