Climate Change and Urbanization Drive Contrasting Lake Shoreline Dynamics Across China

China’s lakes have undergone substantial hydrological and ecological changes in response to climate change and intensified human activities. While previous studies have focused mainly on lake area, lake level, and water quality, the dynamics of lake shorelines, which serve as critical transition zones between aquatic and terrestrial environments, remain largely overlooked. Here, we present a nationwide assessment of shoreline morphological and ecological changes across China’s lakes from 1990 to 2020. By integrating multi-temporal lake maps with fractal geometry, landscape metrics, and land cover data, we developed a quantitative framework to characterize shoreline evolution and its ecological implications. Our results reveal contrasting patterns between western and eastern China. On the Tibetan Plateau, lake expansion was accompanied by increasing shoreline complexity, with 75% of lakes exhibiting greater tortuosity and ~ 40% showing increases of more than 5 percentage points in ecological land cover. Conversely, lakes in the Eastern Plain Lake Zone showed an overall tendency toward shoreline simplification, particularly during 1990–2015, when ~ 70% exhibited decreases in shoreline development index. Across the three eastern lake zones combined, more than 40% of lakes experienced decreases of more than 5 percentage points in ecological land cover within their lakeshore zones during 1990–2020, while nearly 90% showed declines in cultivated land. These findings reveal distinct regional trajectories of shoreline morphology and lakeshore land cover under contrasting climatic and anthropogenic pressures, highlighting the value of incorporating both indicators into lake monitoring and region-specific conservation and management.