In China, decades of industrialization and growing cities have replaced coastal mudflats, sandy beaches, mangroves, and rocky reefs with engineered structures such as seawalls, break walls, and dikes (1–3). The loss of coastal wetlands exposes coastal cities and communities to substantial damages from storms (4) and extreme events, which are increasing in frequency, intensity, and scale (5). The degradation of coastal ecosystems also threatens migratory birds, which depend on the wetland habitats along their flyway (6). To conserve and restore natural coastlines, policies must prioritize quantitative local assessments of successes and failures and use that information to guide national and regional priorities.