Abstarct: The Nekarood karstic basin, situated in the Alborz Zone of northern Iran, is predominantly characterized by thick-bedded and massive Lar and Cretaceous limestones, with minor occurrences of Elika, Delichai, and Ruteh limestones. Submarine groundwater discharge (SGD) is actually any subsurface flow of water that exists from the landward side to the sea, and it can be said that almost all coastal areas are exposed to this flow. The primary objective of this research is to estimate the volume of submarine groundwater discharge from the Nekarood karstic basin into the Caspian Sea using hydrogeological, hydrogeochemical, isotopic, water balance, and remote sensing methods. Due to the presence of thick, laxyered and massive limestone rocks, good karst aquifers have formed in the region. Analysis of the physical and chemical properties of four major karstic springs in the region (Jezi, Espeh O, KaoCheshmeh, and Senbi) indicates a dominant conduit-diffuse flow system. The water type in these karstic springs is calcium bicarbonate, with electrical conductivity generally below 600 µS/cm. The recession curves for these springs are multi-slope line, and the discharge coefficient ranges from 10⁻3 to 10⁻2. To evaluate the recharge value, as an important parameter in the hydrogeological balance study, information laxyers of factors affecting recharge, including lithology, slope, slope direction, vegetation, joints and fractures, rainfall, karst features, and stream density, were prepared using GIS software. After classification and overlaying these laxyers, a recharge potential map was generated, revealing recharge rates varying from 12% to 45% across the region. baxsed on calculations made regarding the annual recharge and discharge of the basin, it is observed that the annual recharge of the basin is about 172 million cubic meters more than its discharge. Therefore, considering that recharge in this basin significantly exceeds discharge, and given the absence of large springs despite high recharge rates, the likelihood of substantial submarine groundwater discharge becomes pronounced. Due to the presence of large faults in the Nekarood basin, such as the northern Alborz, Caspian, and main Nekarood faults, it is likely that a significant portion of the groundwater in this basin is discharged into the Caspian Sea. In order to verify this issue, remote sensing and isotopic studies were used. baxsed on the results obtained from Landsat 8 satellite images, temperature and salinity anomalies were identified in the potential areas of water discharge into the sea. Although these anomalies have relatively high uncertainty, their alignment with the probable area of water discharge to the sea is important. Due to the small amount of water discharged into the sea compared to the surrounding waters and the uncertainty of the exact location of the discharge, radon gas measurements were inconclusive.