Coastal zones worldwide increasingly face conflicts as societal demands, economic development, including tourism, and nature conservation all compete for limited coastal space. Although lagoon coasts are ecologically valuable and morphologically stable, these remain especially vulnerable to small-scale, tourism-driven alterations. Fragmented monitoring means that many of these changes escape detection, limiting opportunities for effective enforcement. Focusing on eight independent campgrounds along a Natura 2000-designated low-energy lagoon coast (Baltic Sea), we analysed long-term shoreline and land-use changes from 1976 to 2024.This study presents first scientific documentation of unpermitted artificial beach nourishment by private leaseholders, resulting in significant habitat loss, shoreline progradation of up to 60 m, and hectares-gained land reclamation prone to erosion. Our monitoring method accurately identified both natural morphodynamics and unpermitted human interventions, demonstrating its effectiveness for resource-efficient coastal management. The study introduces a six-stage model of campground-driven shoreline transformation and fills a key gap in Integrated Coastal Zone Management practice. By demonstrating how subtle, dispersed coastal interventions can trigger large-scale degradation, we highlight the urgent need for scalable monitoring frameworks to support timely enforcement and long-term protection of ecologically vulnerable coastal systems globally.