ABSTRACT: This study investigated the causes of the salinization occurring in the Tarsus Coastal Aquifer (Mersin) located in the Eastern Mediterranean region of Turkey. Groundwater salinization, which is a critical problem, especially in the Mediterranean basin, occurs as a result of processes and mechanisms such as seawater intrusion, climate change, geogenic effects and anthropogenic activities (pollution and hydrological interventions). In this context, samples were collected from 87 groundwater wells and seawater (Mediterranean) during a field study conducted in September 2020. The temperature, electrical conductivity, pH, salinity, reduction-oxidation (redox) potential, dissolved oxygen, and total dissolved solid values of collected water samples were measured in the field. The major ion and trace element contents (Ca+2, Mg+2, Na+, K+, HCO3-, CO3-2, Cl-, SO4-2, NO3-, NO2-, B, Br, Sr ve Li) of the water samples were analyzed in a laboratory by spectrometric (ICP-MS), spectrophotometric, and volumetric (titration) methods. Thematic distribution maps of the analyzed parameters were created using a Geographic Information System (GIS) software. The hydrochemical facies of the water samples were determined using Piper and HFE diagrams. In order to explain the salinization mechanisms occurring in the region, binary (x-y) graphs were created using the ratios of various major ions and/or trace elements. According to the results obtained, it was revealed that the salinization phenomenon affecting the Tarsus Coastal Aquifer occurred as a result of seawater intrusion, the dissolution of Messinian evaporites (anhydrite, gypsum and halite) and anthropogenic (agricultural and industrial) activities.