This study was conducted to determine the spatial and depth-related trends in salinity changes in Lake Urmia, specifically at the causeway bridge section. The 1,250-meter-long bridge section comprises 17 spans; 221 water samples were collected at three depth levels—0.2, 0.5, and 0.8 of the total depth—during September 2024 and June 2025 under the bridge and at stations north and south of the bridge. Under low-water conditions (September), the maximum, minimum, and average salinity levels in the surface layer beneath the bridge were recorded as 438, 402, and 422 g/L, respectively. Under high-water conditions (June 2025), salinity levels beneath the bridge were recorded as 447, 409, and 425 g/L (max, min, and average) on June 3rd, and 443, 397, and 424 g/L on June 4th. On June 5th, salinity levels in the surface layer south of the bridge were 445, 385, and 425 g/L, while north of the bridge they were 435, 418, and 426.5 g/L; these figures indicate lower salinity levels compared to September 2024. The results indicated that an increasing trend in salinity values ​​from the surface to the depth (a salinity-based stratification process) was observed only at the openings of the U3, U4, U8, and U12 bypass channels; conversely, a reverse trend was found at spans U7, U10, and U15, while mixing prevailed at the other spans. The study concluded that the bridge causes localized salinity increases because it increases shoreline length. In contrast, the flow exchange and dissolved loads between the north and south of the bridge are not interrupted.