The Neretva River Delta is a located in the south of the Croatian Adriatic coast. Several authors in their researches and trials have been discussed the issue of confluence of Croatian rivers, which are flowing to the Adriatic sea, are salinated and so-called well-layered confluence or estuaries.Thereby, fresh water flows into the surface layer above the heavier sea water. Layered river confluence is found at the seas with a relatively small amplitude of sea tides, typical for the Mediterranean sea. The most compelling measurements of this phenomenon on the eastern Adriatic coast are accomplished on the Neretva river because the Neretva area with its augmented water management facilities has a large economic significance for the Republic of Croatia.This study analyzes the data on the state of groundwater salinity in the Neretva Delta during 2015, which was given to me by the Water Saving and Agricultural Soil Monitoring Program in the Neretva Valley area in 2015. The results are grouped according to the metering areas - the lower flow melioration units Neretva River to analyze and show the spatial and temporal processes of salt concentration change in underground water in the field of research. Based on the results of a one-year monitoring of groundwater in seven locations, the aim of the graduate thesis is to examine the ionic composition of groundwater samples taken from piezometers in the delta Neretva melioration areas and to statistically analyze the obtained results and to establish the temporal variability of groundwater slope in the River Delta area. Based on the results obtained, the largest increase in groundwater salinity occurs in the summer months, while the lowest concentration of salt in the winter months. Also, salt concentration increases as the location is closer to the sea. Concentrations Na+ and Cl- proportionally increase with the total salt concentration. Of the analyses carried out, it was observed that the climatic parameters have no direct impact on the salinity of the groundwater. Recently, focus takes places on the problem of occasional or permanent salination of groundwater and surface water and it is becoming increasingly problematic and leads to the reduction of agricultural yields, destruction of fertile agricultural soil and the impact on the sustainability of the entire ecosystem. This problem becomes progressively relevant and requires interdisciplinary knowledge in its understanding and settlement.