Rapid urbanisation in the Greater Bay Area of South China has brought about significant ecological challenges, particularly for Deep Bay (both share by Hong Kong and Shenzhen) and its surrounding wetlands, according to a recent study conducted by the Chinese University of Hong Kong (CUHK) and the University of Exeter. The research sheds light on the urgent need to address the detrimental effects of urbanisation on the fragile coastal wetland ecosystems, emphasizing their crucial role in supporting migratory waterbirds.Deep Bay, located in the Pearl River estuary, serves as a vital refuelling ground for migratory waterbirds along the East Asian-Australasian Flyway. The study analyzed long-term environmental data spanning over four decades, revealing alarming consequences of dramatic changes. Between 1988 and 2020, there was a 30% decline in various water bodies, including mudflats, fishponds, and geiwais (shallow ponds found in mangrove areas). Simultaneously, there was a 15.6 km2 increase in impervious surface coverage, primarily resulting from the conversion of fishponds and wetlands into concrete structures. This change in land use has indirectly impacted the water quality in Deep Bay. The population of wintering waterbirds, as indicated by the Hong Kong Bird Watching Society's annual monitoring data, has experienced a significant decline from its peak in 2008 (90,986 individuals) to a recent minimum in 2022 (48,157 individuals). Notably, certain waterbird groups, such as larids (gulls and terns) and railids (rails and coots), have been particularly affected.The study established a strong correlation between the population of waterbirds and the biomass of the macrobenthos, which includes animals living in or on the mudflat, such as worms, crabs, and mudskippers. These macrobenthos are highly sensitive to changes in water quality. The research also highlighted significant transformations in water quality and changes in the macrobenthos community, directly associated with large-scale reclamation projects and the expansion of impervious surfaces.The growth of the megacity Shenzhen has been a primary driver of these changes, leading to a decline in Deep Bay's capacity to support migratory waterbird populations. Deep Bay occupies a crucial position in supporting migratory waterbird populations along the East Asian-Australasian Flyway. Therefore, policymakers must prioritize the protection and sustainable management of Deep Bay as the development of the Northern Metropolis progresses. It is vital to exercise utmost caution when delineating the urban area boundary. The primary objective should be to prevent further fragmentation of the existing wetland habitats while simultaneously providing ample buffer areas for the preservation of their fauna and flora.To address these challenges, the research team proposes implementing strict regulations and guidelines to manage and mitigate the adverse impacts of urbanisation on wetland ecosystems. They advocate for the adoption of nature-based solutions and sustainable land-use practices, as well as the conservation of key habitats within the Greater Bay Area. Effective conservation strategies require collaboration among various stakeholders, including the government, local communities, and environmental organizations. Furthermore, raising public awareness about the ecological importance of Deep Bay and the need for its protection can be achieved through educational campaigns and community engagement initiatives. By prioritizing the conservation of Deep Bay and other wetlands in the Greater Bay Area, we can ensure the region's ecological legacy and preserve its exceptional biodiversity for future generations. It is imperative that we act now to safeguard Deep Bay and its surrounding wetlands. By finding a balance between urban development and environmental conservation, we can create a sustainable future that benefits both the region's growing population and its unique natural heritage.