Along the northwestern Black Sea coast, diverse types of coastal barriers are widely distributed, formed predominantly by wind-driven wave dynamics and meteorologically induced sea-level fluctuations. The baymouth barrier of Lake Ustrychne lies within the continental part of the Tendra–Dzharylgach system, separating the coastal lake from Karkinit Bay. The absence of coastal protection structures at the barrier enables its morphodynamic evolution to be assessed under relatively undisturbed natural conditions. A retrospective analysis of historical maps (1775–1970s) and satellite imagery from Landsat and Sentinel-2 missions (1980s–2025) was used to identify the evolutionary trends of the Ustrychne Lake baymouth barrier. Shoreline extraction was performed in QGIS using satellite imagery, while shoreline position change analysis was conducted with the Digital Shoreline Analysis System (DSAS). Data from the Global Surface Water Explorer was utilized to assess fluctuations in the surface area of Ustrychne Lake. Cartographic records from 1784 to 1855 demonstrate that the body of water initially developed as an open liman. Following the formation of the barrier in 1859, however, it transitioned into a coastal lake system. Periodic breaching was observed within the established barrier. Historical sources document breaches in 1956 and 1972, while satellite data indicate their occurrence in the eastern part of the baymouth barrier during the 1980s. Since 2001, the barrier has been undergoing a process of widening, driven by the gradual decrease in surface area of the lake. The frontal shoreline of the barrier can be characterized as dynamically stable. The barrier underwent substantial morphological changes during Storm Bettina in November 2023. Frontal shoreline erosion and inlet formation have reduced the body of the barrier. The baymouth barrier of Ustrychne Lake has undergone significant morphological and dynamic changes over the past 250 years. Its sensitivity to hydrometeorological forcing is highlighted by periodic breaching events and shoreline fluctuations.