The temporal and spatial changes of surface and underground water interaction in wetlands, as one of the important aquatic ecosystems, are very numerous and complex. In arid and semi-arid environments, where the amount of atmospheric precipitation is highly variable and significantly less than the evaporation rate, underground water is the main factor in maintaining the balance and environment of wetlands. In this research, an attempt was made to investigate the degree of vulnerability of this valuable ecosystem by better understanding the extent and manner of changes in the interaction of surface and underground waters of Qaragheshlag Wetland. This wetland is a type of coastal wetlands and is located at the end of Mardoukchai and Zarinerood rivers in the southeast of Urmia Lake. End wetlands, such as this wetland, suffer more damage than other wetlands if they are exposed to salt water intrusion due to lack of salt removal mechanism. In this research, by drawing the direction of the underground water flow at different times, it was concluded that Qaragheshlaq wetland is fed from its upstream aquifers. Using Darcy's law, the amount of underground water entering the wetland in the water year 2014-2015 was estimated to be about 0.738 million cubic meters. In another method, using the amount of stable isotopes of deuterium and oxygen-18, the amount of groundwater entering in the mentioned year was estimated as 0.802 and 0.558 million cubic meters per year, respectively. The evaluation of the water balance components in Qaragheshlaq wetland shows that about 20% of the water in this wetland was supplied with underground water in the water year 2015-2014.